How do you boil water when you don’t have electricity?

I’ve been thinking about this because of possible brown-outs, food shortages, and mandates. I’ve got food stored up but it will need boiling water. Of course you can buy cheap camp stoves, but I wanted to understand the basic principle of making an efficient stove that isn’t going to require fuel you have to keep buying. The first video does just that. The second shows an easy way to make a safer rocket stove. The third video shows how you can use tea candles (very cheap and light) to cook with. You’re going to need at least 8 tea candles to get a cup of water to boil in a reasonable amount of time. Maximize the surface area of your pot as much as possible, and have a lid to keep the heat in.