First ya gets a can like this.

...and a church key like this.

...use the church key to cut about 8 holes at the base and top of the sides of the can.
...get ya a candle and put it in the can and light it. Ya can then put stuff in a larger can and heat it pretty well with just a candle.
...ya can use a canteen cup to sit on top of the can if it isn't one of them new tupperwear canteen thingy's like they use today.