Plastercat,
I never saw the paperclip trick in the army. A lot of times we didn't have electricity when we were "camping out". :-)
We used something much safer. We burned plastic explosive . . in small amounts (about half the size of a marble). It burned hot and would heat up a canteen cup full of water in a hurry. You can also screw the detonator out of a hand grenade and pop the cap off the other end (It is pinched on, like the cap on a bottle of soda), so that air can get in from the bottom. When ignited, the explosive shoots out a flame like a blow torch. That works well for heating up a bunker on a chilly morning.
Live simply, love generously, care deeply, speak kindly.
Cowards are cruel, but the brave love mercy.
"The purpose of life is to contribute, in some way, to making things better" Robert F. Kennedy