First tip: Don't worry! Your dog will pick up on it if you're anxious about her behavior.
Second of all, Florida has full access rights for service dogs in training. I know for a fact that there is a SD school down there that takes their puppies on a "field trip" to Disney, so I'm sure if your pup plays the dork and barks at Mickey, it won't be the first time it's happened.
The tips I can give you are basic type things:
Invest in a collapsible water bowl. It can tuck into a pocket or bag and you won't even notice it's there (my dog has a bag on her vest and carries her own.) You can fill this up at water fountains or bathroom sinks and they're SUPER cheap to buy online. We got ours for only FOUR dollars-- sure, it's orange, and I didn't want orange, but hey!
I also suggest looking into either some warm-weather boots, sandals (yes, they make them) or this stuff called Mushers Secret, which is a wax you rub on the feet and it protects them from salt and heat. We are probably going to get sandals for her-- make SURE whatever you get has no insulation because if it does, your dog can overheat very easily. We like the sandals you can find online-- this depends on how big your dog is-- because they offer protection from the hot blacktop but they do not trap heat in the boot.
If you can swing it, opportunities to rest are really important. Even if it's just an air conditioned stop at a restaurant midday, it will give your dog some time to recharge. Even better is a midday nap, but that's not always possible, so my plan is to take it slow, do lots of shows and restaurant seating, and give my pup time to relax in line and things.
On the topic of keeping cool, at the very least I suggest a cooling bandana or something like that. There are cooling vests/jackets that I am looking into for my girl because I don't want an overheated dog-- this happens very easily. You can get them online and at pet stores, and they will help keep your dog cool. Depending on the kind of dog you have, you might even look into getting their hair cut short-- poodles, maltese, yorkies, etc. all these dogs don't have a problem with short cuts. If you have a double coated breed-- lab, border collie, german shepherd, etc. DO NOT do this! Shaving a breed like this will actually make them hotter because their hair is insulation from the heat.
There are energy dog treats you can get also-- again online or, if you're particularly into cooking, you can even make them yourself.
http://hubpages.com/hub/High-Energy-Biscuits <---- Here are some recipes. I plan on making some just to pop her one every once in a while, if I notice she's starting to get laggy, and you might even want to pack a midday snack for your dog, depending on how often she eats at home. On that note, treats are important to bring along beacuse it's a high distraction environment, with lots of new things, and being able to reward your dog for focusing on you will go a long way.
Be prepared to have to "child swap" if there's a ride you and the rest of your family would like to go on, but the dog can't. Disney is notorious for being very accessible so many rides are ones the dog may go on.
4D rides and shows are something you want to also be careful about! I know of someone whose dog was startled by a sudden puff of air from under the seats... right where a service dog would lay, and he couldn't relax until they left the theater. Poor guy. Speaking of shows, watch out for the noise levels in some of them! I'm paranoid about my dog's ears, though, and will be investing in a pair of Mutt Muffs.
There was one more thing I wanted to say but I cannot remember what it was...

I'm sure I'll report back and edit this post when I actually do!