Hi lisa-1965, welcome to Cruise-Chat! Congratulations on your up-coming cruise! We didn't go to a beach in Montego Bay, we went on an excursion through the ship. A lot of people have suggested doing Sandals with a day pass there. IslandCruz is spot-on about Seven mile, easy to get to, but you can't walk. It's so beautiful there. Please do check out our Caribbean Port Chat section. You can use your "find" feature in the upper left hand corner, type in your ports and it will pull up all the posts made. You might find something that will interest you.
Please feel free to ask any questions you might have, we'll do our best to answer them. Best wishes!