In addition to the options mentioned (tea lights, Jet Boil, etc.), I’d add Sterno. I have a cheap folding camp stove that uses Sterno, and I’m pretty sure it’s sufficient to boil the cup or so of water needed to cook freeze-dried, backpacker-type meals (or heat a can of soup), especially if using a small, thin-walled pot with a lid. I’ve been making a bunch of backpacker meals, and I bought the Mylar bags to put them in (with food-grade oxygen absorbers). You can add the boiling water directly to the Mylar bag and let it soak for 10 minutes or so. I also saw a video of a thru-hiker who made her own “pot cozy” out of reflectix insulating material. That way she’d just boil water, add the food, and put the pot in the cozy to finish cooking, saving a lot of fuel. In an over-abundance of caution, I’d still crack a window and make sure my CO detector’s batteries were good. I had to come up with something because my prewar NYC apartment building has been without gas for cooking for a YEAR (finally getting that fixed after being postponed by COVID). So I’ve been cooking with a hot plate, slow cooker, and microwave. If the electricity went out, I was definitely screwed, especially if the food supply chain got wonky at the same time. That’s what turned me into a prepper!