I have an aquapac - its a little blue waterproof case on a lanyard that you can wear when you are swimming. It's big enough for your key to the world card, money, and even a small cell phone. It is truly waterproof - my mom took it on their recent Hawaii cruise and loved it! They do make camera aquapacs, but I didn't like the one I looked at (it was a bit too bulky), so we are bringing a disposable underwater camera. I figure that will be with us and if we don't want to use it, I'll leave it in our beach bag under the chair or under a towel. They also have some plastic type cases on lanyards that you can get - I have one from my parents' cruise for my husband to use (he is doing the 12 metre regatta and I am not). It says Royal Carribean so I'm certainly not using it!
I got my aquapac online, they sell them through e-bags and I believe LL Bean carries them as well.
Michele