You may want to invest in an underwater camera to document your snorkeling and scuba diving. The throw-away variety will not capture the full clarity and colors of the reef and fish, but it is much less expensive and portable and will do the trick, especially in shallow waters. If you have your own snorkel gear, it will definitely get a lot of use. However, there is usually snorkel equipment for rent on the boats. Though land excursions are possible, most cruisers actually spend most of their time in the water when they are not on the ship.
Boats gravitate toward similar ports in the Western Caribbean, though the order of stops varies.
Jamaica, primarily Ocho Rios, is one of the main day stops. One of the highlights of any excursion in Ocho Rios is the 600-foot waterfall, Dunn's River Falls, which cascades down rocky terrain to the Caribbean Sea. The staircase-shaped falls are a fairly easy climb, or can be reached by mountain bike. Bike tours are mostly downhill on uneven terrain. Another option is a horseback ride from Chukka Cove along the coast, which includes the opportunity to ride bareback on the beach.