Ew Evil Cannon....
Anyway My husband and I shoot for Theme Parks Magazine and have tons of experience carrying cameras (Nikon D100 and a larger Nikon Coolpix plus lenses) around parks all day, its a good workout I'll tell you that.
First, probably not a good idea to take it on roller coasters, and stuff, what we usually do is carry it around for a couple of hours and then take it back to the car (trunk) after that. Otherwise you will be breaking your back no matter what. Also don't worry about all the lenses, bring the smallest lense you have and only that and one or two batteries. Probably a good idea to invest if you dont have one, a comfortable, chest strap camera bag (one that will wrap diag across but will also be comfortable on a shoulder). I honestly right now am at work and can't think of the brand we use, but will post later because they are not to expensive and very comfortable.
If you dont want to do a bag, then get a comfortable strap, the plush, black camera straps you can get at almost any camera store (Ritz Camera, etc) are much MUCH better then the standard one's that Nikon/Canon gives you. TRUST ME THE $20 is WORTH IT.
If you want to ditch the camera bag make sure you wear something with pockets. Usually what I do is, ditch the camera bag, take the camera, and a couple of batteries with me, (I also have one 500 MB card so I dont have to change that), and stuff the small stuff in my pockets (with baggies!), If you have cargo pants/shorts they work very well, anything with pockets is ok though.
One last thought... bring a disposable camera with you if you want to have photos after you dump the bag of bricks .... excuse me CAMERAS off at your car. Sometimes this might even be a better option to trade off a whole day with. You know one day Cannon next day light disposable. I love my Nikon but disposables are worth there lack of weight in gold and now quality is pretty good. Fuji's are cheap, quality options. No matter what get these before you go, Disney marks them up bad, actually all parks do this.
Enjoy your trip!
Jennifer