Well since you have your van, just take almost everything out of it, and don't stress. Most of what is in there you don't need, and anything you really DO need and forget can be purchased at
Walmart in Orlando.
My philosophy for travel now that I have kids is that I bring enough clothes for about 3 days, tooth brushes, toothpaste and a comb, my camera, my tickets and my credit card. The kids and hubby each bring a game boy, an ipod or something of that sort, and I bring a book.
Thats it.
I've realized that no matter how many clothes I bring, I end up doing laundry in the hotel at some point because someone throws up, wets their pants or gets covered in mud. So now I just plan to do the laundry at least once on each trip...and that cuts the clothing pile at least in half.
I used to bring snacks for the duration of the trip, but most of the time they don't get eaten because the kids would prefer the yummy treats available in the park over the half squished goldfish from my backpack. Besides that, I have no interest in lugging a bunch of food and beverages around the park all day. If they want some snacks in the room, Walmart or a convenience store is never far away.
I always end up needing to stop at Walmart or a Pharmacy for something anyway, so I might as well plan for it and make my packing and travel time simpler. Orlando is a busy metro area with lots of stores, its not like we are going camping miles and miles from civilization.
And if your van is less full then you'll have more room for the kids to spread out so you won't hear "He's touching me!" on the ride.