Idea for a system that don’t use coins (zombie campaign)

So I’m going to end up doing a zombie campaign and I do have idea for like some towns take ration cards as there way of money but that only works for some towns control by well the military and I what to ask is there like any other ideas like a item or something that holds value but can still be used? And if so what would like the coins to (ITEM) valuable ratio well I can finger that out