Survival Paint Can Heaters
A paint can heater is just a metal can, a roll of toilet paper inside and a bottle of isopropyl rubbing alcohol ready to soak the toilet paper roll. You then light it and it burns slowly so you can stay warm in an emergency, boil water and even cook food on top of it. The can does not need to specifically be a paint can, any can that you can fit a roll of toilet paper into should be fine.
To put out the flame you pop the paint can lid back on top of it and reuse it again in the future. Take caution as the can gets EXTREMELY hot.
Original page that I found with it: Survival Paint Can Heaters