Ammo cans have relatively sharp edges on the bottom so if you are carrying some in a backpack a good idea is to put a towel or something under them as padding, for if you were to slip on a rock with unpadded ammo cans in your backpack, and put your hands down to stop yourself falling you could get a finger squished between the rock and the ammo can, with all your weight on top of it.
Any other cautionary tales, please post them