In Grand Cayman, if you are into snorkeling, look into booking Captain Marvins to Stingray City...they stop there between the times the shore excursions from the ships arrive, and you also stop at a couple of other places to snorkel.
In Limon, I would do some research into what you want to see, then hire a taxi to take you there...negotiate the price before hand. All Costa Ricans speak english very well - they are taught in English half of every day in school.
Ocho Rios - I stayed on board and enjoyed the day!