I've bought a few things in advance myself. Yesterday at a liquidation store, I found lots of Disney stuff and got DS (7 yrs) a daffy soccer outfit for 9.99 and a sweatshirt for 4.99. I also bought my daughters Disney sweatshirts on clearance at JCPenney. Now they won't be begging to spend their hard-earned money (I slave labor it out in advance -

on clothing, which give us more time for rides, etc., rather than searching for the infamous sweatshirt that falls within their daily budget.
They each have a set daily amount, and have learned from previous trips how to budget it so as to get the most for their $. I don't get much begging beyond that set amount (even from the 7-yr-old, who can visit a museum gift shop with his $4 and understand how to spend it wisely on what he really can afford). This is our once in a lifetime trip to Disney (maybe ?!) so I'm not going to expect them to come home with much of their own $ afterwards. They already contribute to their personal stock portfolios with birthday money, earned money, but like me, when on vacation, they want to gets a few things that are special to them.
I also bought a lot of pins on ebay (40 for $70, which I think was a great deal - probably not high-demand collector pins but when you don't have any . . .!). I plan to give some to the kids, but also to complete a few of the collections that are started in these 40, then come home after our trip and sell them on ebay to recoupe some of my losses! Isn't ebay addictive? And I bid the same way, counting out the seconds until I press "submit!"