centerfires? signalling for help when a horse threw me and broke my knee. comes to mind right off. coyotes, woodchucks, turtles, fish, those all require many boxes of rounds on good days...those MTM 100 round boxes work best for us for those days, anytime its less than a box or two I use those tri fold elastic bandeded jobbers already mentioned, they wear out but are cheap to replace..other times more ammo than 4 rounds carried?..anytime I am in the bush and there are guerillas, gorillas, or anything about that can claw me bite me or eat me in large chunks...I dont mind dying, I do mind dying for lack of shooting back.
I mainly hunt with flinters so carry about all I can comfortably carry at one time, maybe 100 rounds worth on round ball, half that in shot., which is about a pound of powder to go with that.