In the past I would always take a small point-and-shoot camera. Just recently I bought a small digital camera which I intend on bringing. In addition to the small camera case, I bring a large ziploc bag which I always put the camera & case into right before going onto a water ride. If I am carrying a backpack, I will put the camera (already inside the ziploc) into the backpack for added protection. Instead of a second camera, I usually bring a second set of batteries with me as well as a ton of extra film (or for my next trip, memory sticks). I make sure to purchase them before leaving because I'm sure they'd be a lot more expensive in the parks. My husband will be bringing his fancy large digital camera which is a single lens reflex because he wants some really good quality shots. As long as he doesn't make me carry it, that's fine! I like to bring small, lightweight cameras so they are not a burden to carry.
Hope this helps!
-Laura