I picked up a package of these while I was down in Portland today.They were standard issue for German military kits as far back as the second world war.
One little tablet will burn for 10 or 12 minutes and is enough to boil a pint of water for coffee or rehydrating freeze-dried food.
The best part about them is they weigh next to nothing. They will burn anywhere. Even in the snow. And you can punch a couple of holes into an old food can and make an instant stove.
No… Actually the best part about them is the German word on the box. I read it as “F0CKINBURNINSTUFF”.