I think that with that large of a group someone should speak up and just make sure that everyone is on board with how the system works. Let everyone know what they are entitled to and ask that people keep track of what they use.
Sure it's a pain but it will help with issues later. Also, with this many in the group, I'd probably have the adults keep the cards with them. I can see kids, especially teenagers, going crazy and using up all the snack credits in 2 days! LOL!