My problem is a good filtration system for my get home bags. Because the bags are stored in the car, they are exposed to freezing temperatures in the winter, which renders most of what you reviewed useless as the filters are destroyed if they are frozen. Perhaps one of these is not susceptible to freezing? I haven’t gone through every single one, but from what I have found so far they all have that problem. Right now my thought is coffee filters for large particles and water purification tablets (can those be frozen?). Any thoughts?