The best answer is to take it with you because then it's everywhere you go. Most rougher rides have a compartment to put such items. The plastic baggie idea is good for the wet rides. Most rides are pretty easy and you can manage the camera pretty well.
You can take turns on the rides that are more damaging and then you don't have to worry about it. It's a little hassle but that's the price you pay for pictures. If you can use the standby lines it doesn't take too long. I know this takes a little of the magic out of it but I love having my pictures later; so, it's worth it to us.
Some will rent lockers but then you have the hassle of getting the camera back when you want it, etc. And of course, you will be the farthest away from it when you want it.
We are lucky in that we stay on-site and we stay for long stays. With that in mind we have days we don't use a camera and then we go on all the rougher and wetter rides. Also, there are times we go back and forth from the resort and parks; so, we will plan our day accordingly with the camera.
Don't keep anything of value in the back pack and you should be ok leaving it in a stroller, etc. If that's not the case, then you have to follow the guidelines above for it.