Love your idea biddlesby. We have a fire similar made from an old paint tin.It is called a comet. This was an idea from a book i read more than 30 years ago. The best one is 5 litre size but i'm sure that it can be scaled down to go in a backpack. Holes are made in the sides at the very bottom of the tin. Experiment with the amount and the results improve the fire inside. The tin must have a metal handle, and to this handle is attatched a 3' piece if wire (you may get away with line but i've never tried). This is where the name comes from and the bit i really like. Once the fire is lit in the bottom whirr the tin around your head and hey presto a lovely cooking flame! If you add a handle to your cooker you have a combicomet!!
My original kept me very warm for a winter in the footwell of a morris van but that's another story.
