Your cruise is probably just a warm memory by now, but I would highly recommend Dukoral for anyone going on a Caribbean cruise, regardless of which excursions they take. Dukoral prevents the kinds of illness you can get without even leaving the ship! I was told by my travel medicine specialist that it prevents 90% of all causes of tourist diarrhea.
You take the first dose 2 weeks before you go, the second a week before and the effects last for 3 months. You drink it like a raspberry flavoured fizzy beverage, not at all unpleasant.
For me it is even covered by my drug plan
"Dukoral provides the best protection against the most common cause of travellers' diarrhea," said Dr. Suni Boraston, travel medicine specialist, Vancouver BC. "I have patients who have taken all of the necessary precautions -- drinking purified water, eating fully cooked and hot food and peeling their own fruit - and have still been affected by travellers' diarrhea. Dukoral is another way for us to help our patients have an uninterrupted vacation or business trip."