buy postcard stamps before you leave home. As you wait for shows or parades, have your older son write himself a note and drop it in the mail at your hotel. It will be a nice little journal of his trip.
Give him a disposable camera or to, too. My 9 year old came back with some incredible shots...things I never would have taken a picture of!
Be sure to take a toy from home for each kid...the hotel maids will make a cute little display each day of your stay. Let your son photograph this so you'll remember!
I'd strongly suggest buying a lanyard wallet before you go. I know Land's End sells them. They will hold your room pass, tickets, FPs etc. Things you need handy and won't want to have to dig to find!
WalMart and Target have water bottles that have clips on them...you can hang them from your belt if needed. Give your older son his own fanny pack so he can carry snacks for the day.
One suggestion...if your son has a favorite character you might have him write a card or send a postcard to the character telling him/her the dates he's coming to visit. It might score you some freebies, you never can tell. When we stayed at Movies they had a balloon bouquet and a "personally" autographed card from Woody and Buzz waiting for my son at check in...free! All because we'd sent a birthday photo from his Toy Story themed party along with a request to be placed in the Toy Story section.
Give your son a roll of quarters and a handful of pennies so he can collect squished pennies along the way. You can buy a book to store them in at the park, too.
It's really humid down there, so you might consider taking one of those 3 compartment containers that has a quarter-sized round lid on top. It will hold enough formula for 3 bottles. That way you won't have to carry a can. Another thought...this might be the time to "forget" about formula. I found that my older son was less resistant to change if it accompanied an adventure.
I found my kids enjoyed the parks more because they knew what to expect. If you don't already have Beach Party at DisneyWorld and the Campout video...and the
Disneyland sing-along, get them and talk about what they show. Be sure to let your older son watch the free planning dvd a few times, too.
My younger son saw the gold Dumbo online and made up his mind it was a must-do. Luckily, we got to ride it! (By dumb luck...it was the Sunday of Memorial Day weekend and the line had to be an hour long...but it made his trip to have that little dream come true!)
Also, let your kids collect souvenirs along the way. We came back with 50th napkins, a tinkerbell popcorn box, and a variety of ticket stubs, postcards, etc. All of which I used in the kids' scrapbooks.
Hope some of that is helpful info!