On Ship the US $
some islands use the US $
Some use caribbean $
But all islands will take the US$
However We found that if you take your debit card and use the ATM you will get local currency and for cash you can a good deal if your not to shy and dont need a reciept.
Dollars for both on the ship for the casino and for ashore visits/excursions etc. Best buy dollar traveller cheques before you go to get the best rate the pound is slightly up on the dollar today. Whilst ashore you can also use your credit cards. Whilst on the ship all your drinks/wine/photos etc are charged to your seapass so you are effectively operating in a cashless society for the duration of your cruise. If used your credit card to settle your ship account let the credit card company do the conversion and don't opt for the cruise ship to do it as you won't get the best rate.
We just got back from the RCI Western Caribbean cruise. My advice is take US dollars. The ship takes US dollars and the ports of call in the Caribbean widely accepts the US dollar. We went to Jamaica, Grand Cayman & Mexico and using US dollars would actually give you a better rate than if you bought Jamaican dollars, Cayman dollars & pesos.
Hope you have a great time!
Bring shorts and t shirts thats what you will wear every day bring evening wear for formal nights
adn smart casual clothes for all other nights dont make the mistake of bringing to much .