In general exactly what others have said.  Stop if you are in a safe location or get yourself to one and stop.  Layer up, it is easier to stay warm than to get warm (obviously location and time of year dependent).  If you are really lost activate whatever SOS device you have, which to be perfectly honest you should have in this day and age.  The versions that allow two way comms are best, like the in reach or spot x.  Once you do that STAY WHERE YOU ARE.  Signaling with a whistle/signal mirror are also very helpful.  Also make sure some bit of gear is bright, it could be your pack, a pack cover, tarp, or jacket, or all the above.   More importantly there are some ways to help not get lost.  First periodically look back the way you came, this can help if you get slightly misplaced to retrace back to a last known area or trail.  Modern phones with a  good outdoor map program with the maps downloaded are great.  Just remember to keep it in airplane mode, which will preserve battery but the gps receiver will still function.  Carry a compass and map as backup (also learn to use them).  Also you can use something like fatmaps prior to your trip to get an idea of terrain features, which is especially useful in mountainous terrain. I also always have 2 headlamps, one really bright primary and one small and light one as a backup.  The backup usually goes in my first aid kit so it is easier to find and even switching packs I will at least have that one.  

I also highly recommend having the SMA to BNC adapter.  Then you can use a magmount antenna in your car, or a base station like a J pole at home, and then signal stick while portable.   The SMA connector was not designed for repeated antenna swaps; size and mass were bigger design constraints for it.  The BNC however was designed for repeated reconnects.  I use the signal stick and the Diamond SRH77 with a 2m bandpass filter (some locations here have some serious interference issues when doing summits on the air). 

One of my friends who is a full time guide loves his heated gloves from Outdoor Research for ice climbing.  It allows him to wear a thinner glove while climbing without getting cold, which aids in rope manipulation and getting a nice grip on the tools.  Though in reality a thick belay mitten is just as warm.   I also know that heated undersuits are common in cold weather drysuit diving, again because you have a limited space you can use for insulation.  I don’t know about other brands or versions of heated clothing so my knowledge is limited, but to me it seems best in applications where you have to sacrifice loft for a specific reason.  So it might fit into your plan, for example the gloves for high dexterity tasks during the day, or whatever.  But it would still need to be paired with some high loft versions as well to really keep you warm.   For very cold climbing days and expeditions we also use down puffy pants, might be worth looking into as well.  For example these are what I use. 

I have been in that situation a few too many times (while off duty).  The most recent situations were a cardiac arrest at a friends wedding where I lead the response.  There were two RNs there as well, but with less emergency medicine experience.  I have also helped several hikers, some injured who needed some supplies, and others who got into dangerous terrain that they weren’t prepared for.  Being a climber heading to some technical routes in the area my buddy and I roped them up and got them to a safe trail.  Also assorted motor vehicle collisions and motorcycle accidents over the years.  Since I am such a sh*t magnet I have a full jump bag in my car, an IFAK in my backpack, and a swat-t and cpr mask in my pocket.  

Hey Tim, I am on the younger end of the spectrum, being in my late 30s.  We face a ton of challenges that you enumerated well, but remember we currently have the best tools ever to deal with many of them.  For example the technologies that went into the vaccine development and testing weren’t really viable even a decade ago.  Not only the vaccine itself, but the AI/ML techniques used to design the trials that allowed things to proceed rapidly.  We also have amazing abilities to utilize AI/ML in design of efficient power generation systems that we alone can’t come up with.  We as a society just need to start picking off problems, but also be ready for a rough road along the way to fixing things.  It is really the human factor right now that seems the most unpredictable and dangerous to me.   Stay healthy, learn, contribute to solving some major problem, and find something that you enjoy that you can make a regular part of your life right now.  

I do a lot of technical ice and mountaineering type objectives.  So in those cases crampons aren’t a nice to have but are essential.  Most of the winter hiking I do I use an aggressive pair of snowshoes like the MSR evo ascent, or micro spikes.  If I am doing some gully climbing the crampons end up being used incase I run into some ice bulges.   trekking pole -> microspikes or snowshoes ice axe or ice tools -> crampons   is kind of how I generally operate.  

Yes, that is good if you have time, but if they have altered mental status or in other ways are in extremis I wouldn’t not bother wasting time on taking boots off before.  You will probably be spending some time resting in the shade after, so you can let boots dry out.   Also another reason I almost never use boots outside of winter and stick mostly to approach shoes.  I can get them wet and they dry out fast enough that I can just keep moving.  Obviously need boots if you have to wear crampons or other traction, but then you are unlikely to have severe heat injury.  

I started out hiking when I was younger, but then started climbing in a gym.  My wife has been climbing since she was a teenager so we do that together.  We took a few classes together, mostly for anchors and those sorts of things.  Then I started on the AMGA progression and have started going out on guided days more to work on skills I need for upcoming courses and exams.  So I learned initially over time and reading, but recently it has been more formal and much more accelerated.  

I use to be much more prepared when I worked in EMS full time, kept a 72 hour kit in my car with extra uniforms and supplies.  Since then I have been fairly well prepared for wilderness and medical situations, since I do a ton of climbing and mountaineering. But really the last year and a half has gotten me to prepare more broadly and for a longer term situation.  Moving back to NH from Boston has also made it much more practical as well for some things like gardening which I enjoy anyway.

Also remember if you STOP sweating in a hot environment it is time to seek some medical assistance.  

There are a few parts to this that are going on, heat injury, dehydration, and possibly some sunburns.  For the heat injury part cooling off, including active cooling (especially if there is altered mental status) is key.  Get out of the sun, into a cool spot, and use water to help the cooling process.  For example wetting clothing with water, or if in a wilderness situation getting into a stream or a lake (if safe to do so and with help if available) will drop temp fast. Remember this is for environmental heat injury and not fever (especially in pediatrics).   Prevention can go a long way.  The umbrella and hat a great ideas.  A canopy or sun shelter is also good depending on situation.  I do a lot of climbing on sun exposed slabs that are long and one of the keys to not getting as hot or sunburned is actually a long sleeve sun shirt.  They have UV protective ratings, and are light colored.  They also are more of a tech wick type material so help with cooling through facilitating evaporation.  I love the hooded ones, but there are also button up ones that are actually a bit lighter and have nice venting in the back.  This is a massive improvement over any sort of sunblock goop. For the dehydration part it is always better to go into a hot day in the field with a good hydration status, however most of us know beer is sometimes too tasty.  So constant hydration throughout the day is key.  Trying to catch up after getting dehydrated, even a bit, is hard since you might be trying to stuff more water in than the transport rate through the gut.  The transport rate is actually affected by the presence of sugars, so things with small amounts of sugars are useful, however Gatorade and the like are too heavy in sugars.  Look for things made for endurance athletes instead.  In situations where you feel you are really starting to get dehydrated, urinary output is diminishing, and the such consider switching to a WHO rehydration salt mix.  All of my wilderness med kits have some WHO rehydration packets because dehydration can come up fast out in the field.  

I personally would be cautious about over optimizing the primary kit.  You might plan on going to a hotel, but instead end up in the woods, or a large evacuation shelter and wish you had some of your other items.  For me making the main kit universally applicable but not necessarily optimized is key, that way it is easier to adapt to the situation.  And then throughout the seasons add and subtract sessional items as appropriate.  Having secondary add ons isn’t a bad idea, as long as your main kit hasn’t removed your ability to handle a wide range of situations.  For example still having a lighter, a contractor bag and cordage for fire and shelter even though you might have a secondary kit with a tent and sleeping bag.   Another thought on mentioning the USB cords as a plushy add-on, my main kit has the means to keep my phone charged (power bank, solar panel, charging cable) and also an OTG adapter and a USB drive with useful and not so useful books in PDF form.  The phone is a great tool, and having a bunch of books will be nice for the amount of hurry up and wait that can happen in a survival situation, even in the woods.   But like others have said run scenarios.  Train with your primary pack, go into the woods and spend the night.  Set up in a garage for the night like if you were in an evacuation shelter like a school or community center. 

Some baking soda added to joints with superglue makes it less brittle.  Common trick used when building miniatures for table top gaming.  Also if you buy from someplace that caters to gaming or model aviation you can get different thicknesses of CA, which is super useful.   Along the hot melt line there are low heat and high heat (industrial) which I suggest having both on hand.  I have a battery powered hot glue gun that can handle both.  I also keep a ton of hot melt designed for arrow points since I do a ton of archery.  Regular hot melt can work, but it isn’t as strong.   I also love artificial sinew for leather and heavy duty clothing sewing.  It is super strong and nice to work with.  I keep a big 1 lb spool with my leather crafting supplies and a bunch of different cutting needles.   For high strength rope if you know any climbers you might be able to score a retired rope, slings, or cordelletes.  If it is retired don’t depend on it for life-safety applications, but it is still likely very strong unless it took  a core shot.  I am retiring a ton of soft goods this season and have a bin full of that crap that will mostly get used for training or for my rescue sled.  

I use Gaia GPS all the time as my primary means of planning and navigating in the backcountry.  The different base maps and overlays are super useful.  I also pair it with FatMaps to get a better sense of things pre trip.  Also I think it might be useful when learning to read topo maps to be cable to compare to a 3d representation of terrain.  

Probably a bit light on tools but… standard tool set that came with car jump start battery with compressor fire extinguisher EMT bag trekking pole – mostly through laziness but now that I think of it it is a useful thing to have for efficiency, shelter pole, splinting, other utility tasks snow shovel brush and scraper lighter plug to anderson power pole converter (yes I am a ham) survival kit large swiss army knife ESEE laser strike ESEE mess tin survival kit 2x contractor bags 2x lifeboat rations “pocket chainsaw”

I live in central NH and spend a ton of time up north climbing and backcountry skiing.  I use the hexamine tablet stoves as my primary light and fast stove, though one that is more efficient than the little box stove.  Specifically the flat cat stove system.  It works great.  I also have one of the box style ones posted above in my bugout bag.  From my experience spend some time playing with them, and carry a wind screen, especially in winter.   I do prefer them over a standard jetboil for extreme cold.  I have had a canister stove fail to boil water in winter when cold enough out.  In winter you really want an inverted style canister stove if you are going with a canister, like the jetboil joule or switch to a liquid fuel stove like the whisperlite.   My car kit currently doesn’t have a stove, maybe it should given how many I own….. I just have a couple of those ration bars, the 3 day ones and figure that is sufficient.  I do keep my survival kit in a pot, so I can melt snow/boil water over an open fire.  Plenty of dead standing that can be processed and also snags to be found in the northeast.