When I go to SaMo and Venice, a lot of the time I'll end up in the ocean in whatever clothes I came in that day. I've ruined a pair of boots and lost lots of jewelry this way. Now I don't wear any jewelry to go to the beach.
If I'm going with the intention of swimming, I'll wear, usually, a girl's bikini bottom under trunks/shorts and a sports bra or (if I don't have anything else) a bikini top. I'd be more likely to wear a shirt in the ocean as well, but in a pool I wear as little as possible.
Next time I go to the beach I'll probably bind (haven't been since I got my binders--damn, it's been a long time) and wear trunks.