We took about $50 in $1 bills for room service, baggage handling and assorted other tips.
A power strip that you can get from the $1 store for extra outlets.
A small pocket flashlight was handy for middle of the night bathroom trips.
A really small purse or fanny pack. I bought a small purse in the gift shop on the 2nd day for I think it was $8 and it worked great for the small case I have for change and bills for the casino and held that priceless sign & sail card. Plus there was room for deck plan and the agenda for the day off the capers.
Instead of a power strip you could take a 3 or 4 sided plub extension. It is a lot lighter and will take up no space. If you just leave the bathroom light on with the door closed it works fine to illuminate the room enough to make it to the bathroom.
Sunscreen! Suncreen! Sunscreen! The tropical sun will burn the hide right off of a rhinoceros!! Even my DH who never burns, lets me "grease him up" I Pre did my tips in thank you cards before I left. That way you are not searching for the right amount of bills on the last night of the cruise. (you can always ajust them if you want!) Take lots of quarters for laundary if you plan on washing any. Go to the talk about "recommeneded" shopping places. They have a lot of good info. Always ask about the drink of the day! Its cheaper!! Join in as much games etc. as you can. It's just more fun! At the art auction the first day, they give you free champagne!(You don't have to buy anything, or even stay for the whole thing!) Relax and have fun!
if you are going with others purchase walkie talkies unless you have cell phones that will work (most do not) with the walkie talkie you can keep in touch with others......the ships are a lot bigger than you may expect.