One year, my MIL gave each of my 4 kids $200 in spending money. It sounds like a lot, and it was (IMHO), but I know better than to stand between a generous grandmother and her favorite grandkids! But one thing we did was tell the kids they had $50 in each park. They didn't HAVE to spend it, but that was the limit. Any money left over would go into their bank accounts.
I found with my younger kids, this was more than enough. They did pick out a couple, meaningful items, and that was it. My older son was ~12, and obsessed with Pokemon. We went into the Japanese department store, and he wanted to buy a ton of the cards--because, you know, you can't get those in every Walmart across America or anything, right? We reminded him of the park limit, he pushed back that it was HIS money, HE wanted to spend it all, and he didn't care if he had no spending money in any other park (this was Day 2 or so). Well, we conceded--it was, in fact, his money, we had just been trying to help him budget.
You know the punch line, don't you? We get to Tatooine Traders in the Studios a day or so later, and he was one broke and hurting camper! He's now 20, and he STILL doesn't learn lessons unless they're painful.