On Grand Turk we took a (carnival)excursion to snorkel with stingrays. The trip was very nice and the barracudas were an extra surprise! The excursion people were nice, informative and generally very pleasant. Again, very accommodating to my elderly mother. I'd take that excursion again without a doubt. Unfortunately, we didn't have time to explore the port area, but there's always next time!
Nassau was our last port of call. This, too, was a carnival excursion. We were transported to Atlantis via bus and then had a walking tour of Atlantis. A big mistake for us because my mother's walking became more and more limited while on this cruise and it was difficult for her to finish the tour. We shopped a little in the port area. I found the prices to be quite high and nothing special. I bought nothing. I would take a snorkeling tour if I returned there.
More 
