Believe it or not but you can boil water in a paper cup. I've seen it done.
Trying to keep things simple.
All silliness aside (for just a moment), I do think it's good to know how to cook, purify water, and stay warm without electricity and gas. It's an uncertain world.
I've never tried the water in a paper cup thing, but it's pretty well documented. Indigenous people all around the northern hemisphere used to boil water in birch bark (basically paper; possibly even more flammable) containers. I don't quite understand why it works; it does have something to do with the heat passing quickly through the bark/paper and being absorbed by water. Water can absorb an amazing amount of heat. A thicker wooden vessel will catch on fire, but birch bark doesn't, as long as the flames don't reach above the level of the liquid.
You can also use hot rocks: Heat a rock in a fire until it's glowing, then drop it in a container of water. Instant boil. The plains tribes in North America used to cook stew that way in cleaned-out buffalo stomachs or even just animal skins. I've never actually tried that one, either. Need to remedy that at some point.
Hmmm...now that we mention it, tomorrow is my night to cook... 🤔