A little thread creep: In the military, before there were Meals, Ready to Eat (MREs), there were C-Rations in cans. There are official ways to heat up both types of meal, but I don't believe people ever used them. We just ate 'em cold or found creative ways of heating them up.

I used to work on generators. Big, jet-fuel fueled, jet engine driven suckers with the exhausts facing skyward. Folks used to open cans a bit, set them on the edge of the exhaust and pull 'em off with tongs when they got hot. (Usually in a matter of seconds.) I was out in the Mohave desert once, and the guys explained how to do this to a young officer. Unfortunately, they forgot the part about opening the can a bit. I had to help clean up the aftermath of the spaghetti-and-meatballs bomb.