For the stuff I was concerned about - like my kttw card, I bought one of those waterproof plastic containers that snap shut, and that you can take with you snorkeling. The other stuff, I decided to just hide in my shoes, covered up with my t-shirt.
The biggest problem that I have had on CC was returning to my hammock, (which I got up very early to get), and finding it occupied. I even WOVE my strap from my fanny pack through the webbing, and found it removed and lying in the sand. I had saved this spot for my whole family by getting there early, and returned to find it taken over! I really don't mind sharing the hammock while I'm gone - but no one asks, they just move on in.
On one trip, I went to lunch and found my
DCL rented snorkeling gear gone! I agree you do not have to worry too much about thieves, just some rude and boorish people. I really don't know where they come from, it seems we never run into them on the ship (I take that back, I do run into them at the pools sometime). But on CC, they seem to come out of the woodwork!