Once there, the only thing we pay for is his meals. If he wants some junk toy, candy, etc., he pays for it out of pocket. We've noticed that when it's their own money he's very picky about what he's going to buy, and it's taught him a very valuable lesson that has spilled over to a regular thing at home.
Last year, he even put so much of his vacation money away because there was a pair of tennis shoes he wanted to purchase once he got back hom. The shoes were $49.50 and he gave me $50 to purchase them for him online. Once I purchased it, he asked for his change back. I happily gave it to him.
We also keep a "change jar" that is really a smaller water cooler tank for stashing change and cash through out the year. So when our kids get an allowance or find money we ask them if they would like to contribute to it. We also empty our pockets each day. We did for 6 months last year and saved $250. We are going on 8 months of saving so far this year and there appears to be double the amount in there althgouh we won't count it until May before we go to Disney in June. We told the kids that outside of their own saved money that we will split up what is in the jar for everyone to take as spending money. They didn't want to work for it at first but I told them I wasn't budgeting spending money so they responsed and it seems to be paying off!
And yes, you have to stand by your boundary of once it's gone, it's GONE! And can't be upset when they ask over and over, it's a great learning opportunity. Just keep explaining it to them and presenting them with their choices and then the results. Easier said than done, right? :)
When they were too small to understand the inflated cost of theme park souvenirs we purchased a few character toys at home at our local discount store and took them with us, wrapped up in colorful paper. Sometimes they received these gifts in the car on the way to the park (especially the first day when they wanted everything they saw the other kids holding), sometimes it was just waiting for them on the bed before they went to sleep. We were able to bypass a lot of eye-candy during the day when we reminded them they had a surprise waiting for them back our hotel.
When they were 12 & 10 they used their own allowance money but could only spend up to $25 for the week. Not only did they have to budget the money, but we asked them to look at their purchase with this in mind: What will I do with it after I get home? We also asked them to walk away from whatever they wanted for one hour and if they still wanted it then they could buy it. Nearly everything in themeparks is strategically placed to guarantee an impulse purchase. I can't tell you how many times they never went back for it after they thought about it! Also, some of the discount stores outside the parks have some great deals and give more bang for your buck.
At 12 & 14 they were more interested in a bag of candy but they still had to pay for it.
We sit down as a family before our vacation and talk about the wonderful things we'll all be doing as well as what is appropriate for everyone to spend, this way there aren't as many bad feelings. We give them a small planner or spare check book register and that helps them keep track of how they've spent their money.
Lastly I believe that a few souvenirs should be part of any memorable vacation. I myself usually come home with a picture frame or holiday ornament, but even if it winds up being something silly or a bag of candy - it's their vacation too. We don't want them to feel bad about their choice. Help your children find opportunities to earn some extra money just for the vacation. Maybe babysitting, washing cars, raking leaves...they'll appreciate their purchases all the more if they've worked and saved for it!