I have left bags out in open sight on land and on the boat and have never worried one bit. HOWEVER, we were assaulted on the Willy T on locals night a few years ago and then returned to our 2 Cats and found that we had been boarded and robbed: They made off with 2 laptops and a handful of phones. I inquired with the Willy T the next morning and they blamed it on the "locals", which were actually a bunch of hoodlums from St. Thomas.

Other than that one thing, we have never had an issue. Never lock up our dingy and usually just leave our bags lying where we drop them. Its a safe place...