I use the tins that hold the explosive cartridges used to drop bombs from fighter jets.
Seriously, think 35mm film capsules, only made of aluminium and with a screw top.
Another solution, and one that's ideal for survival kits, is to stuff it into drinking straws (the big ones you get in fast food joints are ideal) cut to length and melted shut.
it's waterproof and can be split open when needed.