If you have never been to any of these locations, I suggest that you look at NCL Shore Excursions.
(linked a few below). You might want to select by activity level, depending upon your fitness levels.
Note: your Cruise reservation last page shows your itinerary. It should list if you will dock or use Tenders (boats that will carry you to shore off the ship to the port). That does matter, because you will need to make well thought out plans if you book impendent excursions.
We have been on many cruises to these locations, so here is a list of NCL Excursions we enjoyed:
Roatan:
Horseback Ride & Swim = good
Tabyana Beach & Gumbalimba Preserve & Animal Sanctuary = good
West End Ultimate Kayak & Snorkel = very good
Jolly Roger Catamaran Sailing & Snorkeling with Lunch = very good
Harvest Caye:
(Operated by Belizeans, and owned by NCLH ... can be costly.)
Be sure to walk around the island and see the wood carvings, the beautiful pool area, the bird and small animal sanctuary, the locals shops, and the flora and fauna!
We enjoyed:
Stand up Paddle Board Rental Enjoyable
Kayak Rental: Enjoyable
Black Swan Electric Boat Cruise: Enjoyed the peacefulness of this boat ride, a different view of the island.
Luxury Beach Villa: We invited several guests to join us. It was an extraordinarily chilly day, so we did not spend much time in the water. The Villa suited the needs of everyone. We did order and pay for food and beverages while on the island.
Costa Maya:
Passion Island Beach Day We had a good time with friends.
Catamaran Cruise & Snorkel: Very enjoyable (if the weather is decent).
Chacchoben Mayan Ruins: We had an excellent guide, learned plenty about the area, the Mayans, and their ways.
Cozumel:
Passion Island Beach Day: Good day!
Fury Catamaran Snorkel & Beach: Good.