I've always taken a fanny pack to theme parks, and I don't really care if someone else thinks it's too 80s. It's the most practical thing out there, and significantly better than the backpack I used when I had kids in dipes and we went.
The thing I like about the waist packs is that they are really made for this. There is normally a tiny zip pocket at the front for credit cards, the often have 2 compartments which means you can separate your stuff from your kids' stuff, and even the smallest will hold the digital camera, cash & plastic, a small first aid kit, and a small bottle of sunscreen. Plus, you can hook things onto the waist strap, like bottle holders or sunscreen.
also, backpacks make me sweat. Not cool in the Florida heat. The waist pack has very little sweat potential. Just don't get leather - they don't hold up as well and they get sweaty faster.
The other option I'm entertaining, though it's a definite for the boys, is to buy Disney lanyards with coin purses attached. It's against the rules to link you to ebay auctions, but if you search "disney lanyard wallet" or "disney lanyard coin" you will find several of these for $4-5 plus shipping. They can give you funny tan lines too, but you shouldn't be getting too much sun b/c you will NEED the sunscreen in FL. There's nothing like ball games and theme parks to make you look like a lobster.
The thing I like about the waist packs is that they are really made for this. There is normally a tiny zip pocket at the front for credit cards, the often have 2 compartments which means you can separate your stuff from your kids' stuff, and even the smallest will hold the digital camera, cash & plastic, a small first aid kit, and a small bottle of sunscreen. Plus, you can hook things onto the waist strap, like bottle holders or sunscreen.
) 
If my coworkers saw that I'd never hear the end of it! Though most have never been to WDW so they wouldn't understand. 
Whatever else you decide never keep all your money & cards together in one place!!! 
