The funny thing is that the Federation doesn't have money (apparently), but in like half the episodes where they need something, they end up trading for it. And in at least one episode, they trade sex slaves for it (Mudd's Women.) So they don't use money, but they *do* use barter, the thing money replaced... hm.
It seems like it would save a whole lot of trouble if they would just carry money around in the first place.