The Norwegian Army is currently teaching its Border Guard (that being the Russian border, way up in the subarctic north) to drop a tea candle into the bottom of an empty food or drink can, to use to heat up the multi-use "Mountain Tarp" poncho/tarp/bivvi bag/ski-sail/tent they are issued. Without the can, it would be rather dangerous to light a candle inside the flammable bag. With the can, the tarp material won't get close enough to the flame to catch fire, and if you accidentally tip the can over the flame will usually drown immediately.