The US dollar is accepted at most Islands in addition to the Islands own currency. Changing money on the ship from dollars to any local cash is no problem.
They will take your US$ quite happily! Cannot recommend excursions unless you let us know the itinerary. It is very easy to DIY on Caribbean islands if you do enough research.
Having been to the caribbean i would think twice at booking excursions. there are always plenty of local taxis available at the ports and i felt that this was much better values for money.Plus the advantage is this is these peoples lively hood and they tell 100 times more than the tour operators.
The US dollar is best but use small denomination notes as they don`t always have much change in taxis etc. The excursions are quite expensive but with some research you can sort youself out locally for a fraction of the cost.We did 5 hours in a local taxi(8 people)on St.Kitts where the driver took us anywhere on the whole island and his local knowledge was vast, all for $20 each. The same type of excursion was £50 each with the cruise company.Support the locals!!!