Costa Rica: (you did not say which port) if it is Limon, when you get off the ship look for the canopy covered tour table with a sign stating all tour names & prices thus no haggling. We did the Tortugero Canal and Banana Plantation tour for $45 per couple. It included lots of stops for photo opportunites including Playa Bonita, flora & fauna & 3 toed-sloths & monkies. Our driver Humberto, also stopped at a supermarket at my request so I could purchase Costa Rican coffee, vanila and fresh fruit juice. Don't miss buying wooden ware at the pier craft bazaar.
Panama; Limon (?) this is where you want to book a Ship's tour; We did the Ocean to Ocean train trip which was well worth the $135pp. The train is beautifully refurbished, each coach has an English speaking guide with assistants and table & beautiful booth seating. Motor coaches are modern and all airconditioned. The stop at Miraflores Locks was a great way to experience the lock operation of the Canal from the landside. It was onto the Bridge of the America's and the Balboa Yacht Club, then a drive through various towns along the way to Panama City Bay. A light snack, Panamanian coffee and beverages were provided.
Martinique; walk up to the town park and to the seaside. Marie Antoinette's statue is beheaded and probably litered with paint. Ask on board your ship what "color" ferry to take over to Pont du Buc. It is a quaint seaside resort where Le Meriedien hotel is located. Go to the beach there.
Barbardos; outside the port shops building get a private taxi tour to include Harrison's Caves and an Orchid or Floral Orchard plus many other stops along the way. Apx. $30 plus admittance to the caves and orchard.
If you have any question, don't hesitate to email me directly.
Bon Voyage