Pack anything that you would need if you were vacationing at a resort hotel located in the same area or areas of your cruise itinerary.

Avoid over-packing.  Read the dress code section of the literature mailed to you by the cruise line.

If they have a theme night, talent show or formal night, you may need special outfits.

You'll probably need a sweater on deck at night, even in the Caribbean. Inside dining rooms cooled by air conditioning can also be chilly.

Remember to pack comfortable, rubber soled shoes to walk the decks.

You may want to bring a small calculator to help figure the exchange rates in the various ports of call.

If you're a snorkeler, bring along a T-shirt to help avoid having a sun-burned back.

Pack some drinking straws to use to avoid touching your lips to a can’s top.  Especially in port, the tops could be unsanitary.  Why take chances ? 

Always keep any items of value with you. Never put cash, jewelry, medication, travel documents, passports or anything irreplaceable in your checked baggage.  Keep a list of the contents of your checked luggage, in your carry-on bag.

Often, luggage is not delivered to your cabin until after you have left  for your first dinner. You may want to pack a change of clothes for that possibility.

Consider any "one-day" items.  Anything that you would need to make it through a 24-hour day in case your luggage is late or missing.

Keep one and five dollar bills with you for tipping skycaps and porters.  Purse, wallet or carry-on bag, whatever is handy and easy to get to.