We just got back from the 5/18 Eastern. On St. Martin...we went to Dawn Beach...$7per person each way...tons of cabs as soon as you get off the ship. We had read a lot of recommendations off this board which is why we went there. You can rent snorkel stuff/floats/etc. There is a restaurant with burgers (good) and $1 beer. It is on the Dutch side, so not as much toplessness...we saw 3 topless women. The French side has lots of full nudity. The beach is gorgeous, but the day we were there, it was windy and not good for snorkeling, but the water was great to stay in. You can rent chairs and umbrellas for $10 I think (you pretty much have to do this). There are lot of Locals selling wraps, jewelry, etc...you can really talk their prices down in St. Martin...at the beach and at the downtown shops by the ship...great deals for Tropical night...everyone bought clothes there to wear that night...great shirts for men and dresses/skirts for women.
In St. Thomas...we went to Coki and it is great. Great snorkeling. No jet skiing, etc, because it is on a reef and the water sports would mess things up. $7 per person each way. You rent chairs and unbrellas here too. Several places to eat...people walk around taking drink orders. Fairly small sand area, but plenty big. The snorkeling is great...especially on the Right near the rocks...going toward Coral World.
Take plenty of sunscreen...the sun is sooo much stronger down there. We took SPF 45 and still came home slighlty burned.
If you want your hair braided...I would do it on the ship...the ladies on the beach really bothered me a lot...I didn't have mine braided...didn't want it...but they asked me all day. If I would have been interested...I would have done it on the ship before I got to the islands. Plus, the ships clean there combs and equipment and I've heard the locals on the islands don't do that and there have been problems with lice.