We did not do any booked excursions. But I have to say that if I had to do it all over again I would have booked things to do in Ocho Rio's Jamaica and in George town, Grand Caymen.
We loved the beach in Labadee (Hideaway Beach was the best as far as less people). They also have an adventure area for younger people with "icebergs" to climb and slide and water trampolines to jump on and off of. Lots that we saw just walking around.
We loved Paradise Beach in Cozumel. Had the same sort of water activities that you could use for a $7 fee and you could rent jet ski's there as well, but I am unsure of the cost.
Found that there was not much to do in the other ports (Jamaica and Grand Caymen) unless you booked an excursion. In those ports we took time to do shopping and cabs to do sight seeing like Dunn river falls (we did not climb due to leg problem, but it was beautiful). We also went to The Ruin's which has a beautiful water fall right out on the back deck. There was a lot of rebuilding going on, so you should book for those two ports if you can instead, But of course that is just my opinion.
We had a great time no matter what we did. The ship is fabulous and we could have spent a whole week just exploring there. The shows were great as was the food.
You will have a great time.
If you are not a beach person (or people) book the excursions, people we went with loved the jet ski's. No one I know did the ATV's, so I can't help you there.