Can you tell us which cruise you are going on? if its the Caribbean, at a lot of the ports of call, you dont need a taxi (unless you want to go further afield), you can just walk off the ship to the town centre very easil.
You haven't given us much information to go on! Please advise which ship you are going on and which port you are referring to with regard to the Sugar and Spice trip. As a rough guide, British ships use sterling and US ships use USD. If you are on a US ship you could exchange sterling at the desk but get ripped off with the exchange rate.
Sorry new to this, going on Ocean Village,Sugar & Spice trip Caribbean,Margarita,Greneda,St.Lucia,Martinque,St.Vincent,staying a week in Barbados first.
What will the weather be like at sea will I need the tablets.