One good thing about having The Goof not being able to do the big rides is that while others go on those water rides, whoever sits out with The Goof can hold onto their stuff.
Back when we went in 2007, that was not the case though. We didn't have The Goof. We weren't going to leave our stuff anywhere obviously, but we didn't want to worry about our phones, cameras, etc getting soaked (and if you do the rides like we do the rides- they will get soaked).
This is what we did to protect our electronics, etc.
First we put them in zip lock bags. The first day we didn't, and we realized this was a necessary step.
Second, we put the zip lock bag(s) in a plastic travel cosmetics bag. You want a good quality heavy duty one.
Finally, if you have a purse or backpack (I prefer backpack) put the cosmetics bag inside of that. Also, if you have paper tickets- make sure you are putting your tickets in the bag as well. When we went back in 2001 for our honeymoon, our paper tickets got so wet that by the last day, they didn't work for fast passes. 2007 we bought plastic "card" tickets from the Disney Store so we didn't have that problem.
Take a little extra time to protect your valuables and it can save you a lot of unnecessary expenses.