You might want to look at the info on this link http://www.cdc.gov/travel/caribean.htm to see what they recommend. I work in a public health department, and when I went on a Western Caribbean cruise, I asked about any travel immunizations. They told me that as long as didn't eat any foods other than what was served on the ship, I would be okay. But if you plan on sampling local fare, you might consider getting a Hepatitis A vaccine. Contact your local health department - they can answer any questions you might have.
My wife and I are sailing on ms Zaandam to the W Caribbean in about a week on our first cruise.
I spoke with my doctor during a recent office visit. He said that for the durations you are in each port, he doesn't think there is a need to get added immunizations. He did say to heed any warnings about drinkinig water in MX and other places. He suggested bottled water if it was available on the ship.
Just returned from Cozumel, Costa Rica, Panama and had no problems without any shots. Agree that if you go on a rainforest tour, take some bug stuff with DEET, but otherwise, no problems eating the wonderful fresh seafood, salads ( the greenest salad I ever had was in Puerto Limon, Costa Rica - fabulous!).
Everyone that travels should get the 2 shots that make up a long term Hepatitus A immunization. My doctor told me that it regularly occurs even in my midwestern home town! It is the very least you can do for yourself. You should also make sure that your other basic shots (like tetanus) are up to date. I also went ahead and got my typhoid immunization because I have travelling a lot lately to places where I am at risk.
Our upcoming cruise is stopping in Senegal and several places in Brazil. So, we considered getting the yellow fever immunization but I'm thinking that a lot of deet might prevent that. I looked up the incidences of visitor infection and they were low. We will be taking anti-malarials. I've been on a trip where they told us we wouldn't be exposed and we were. I was glad I had been overly careful and shared my deet lotion with as many as I could.
So, if you are not sure what you are going to be doing, you are better off being safe than sick! Put together a good first aid kit so you don't have to spend the money on the ship doctor. As a side bonus, the doxycycline that they often give you as an anti-malarila can ward off many "Montezuma's Revenge" type problems!