I think I'm looking at this question differently than other people. For my family for miscellaneous incidentals (just three of us), I budget $50 a day - that's $400 for a week long trip - I include travel days (varies quite a bit from day to day). That covers tolls, airport parking, theme park parking charges, tip for maid and valet parking if we are staying in a hotel, snacks at parks (not meals), anything we might buy at a drugstore like Walgreens -- sunscreen, aloe gel if someone gets too much sun, anything someone might have forgotten at home, gas for rental car, covers mini golf if we do that, covers little speed boat rental if we do something like that (spur of the moment recreational activities we didn't plan in advance), covers film processing if we decide to print pictures before going home). Typically I come in under budget, but I like to have the cushion budgeted.
DH and I don't get souvenirs, but DS likes these. He's in High School, and I give him $100 for the week long trip. If DS wants to spend more than that, he has his own money he can use. I also let him keep the money if he doesn't spend it to discourage wasteful spending.
When he was little I just gave him $15 a day vs. all the money up front, as he then wasn't so good at planning (more into instant gratification vs. delayed), and I know would have run out of money if he had it all up front. I worked with him if he admired something to save up money for a few days, so he could come back and buy it. Sometimes that didn't work, because he couldn't resist getting something little instead, but that meant he didn't have enough for the bigger ticket item. Sometimes it worked because the bigger ticket items was just so special to him that he passed up the other things. Back then though we had to remind him about what he was saving his money for.
My vacation budget line items are:
-Air
-Hotel
-Theme Park Tickets
-Rental Car
-Kennel for dog
-Special Meals (Any Disney table service planned go here as they can be quite expensive)
-Food (groceries, counter service meals, take out, meals at chain offsite restaurants)
-Miscellaneous -- covered above $400 for the week ($50 per day)
-Money for DS to use for souvenirs -- $100 as stated above for the week