I enthusiastically echo Donna's suggestion to bring personal cards with names, address, phone number and email address. They're easy to make yourself on the computer. Avery has Clean Edge Business Cards, with no perforated edges, for ink jet and laser printers. It is so handy to be able to give them to new friends on the last night, rather than borrowing the poor waiter's pen and scribbling something on a napkin (and then forgetting to give him/her back the pen). We got the idea from a couple of guys we met on the Voyager Baltics cruise a few years ago and have seen many more people using the cards in our several cruises since then.
An extension cord with lots of sockets or a surge strip is an absolute necessity if you bring many electronic gadgets.
Someone on some thread also suggested a night-lite - great idea for making a visit to the WC in the wee hours and not being blinded by turning on the bathroom lights.
surfwearhawaii.com sells excellent Havaa Water Tees that are completely sun-proof, yet dry in a very short time, two advantages that cotton T-shirts do not offer. The guide on our shark and ray snorkeling trip really wanted mine; and I would have given it to him if the result would not have been my sitting there with my all-to-ample flesh exposed to the sun and the view of the other passengers on the little boat. Yikes!!
Finally, we like to bring photos of our kids (furry, four-legged ones) in nice leather frames to put on the little shelves next to the TV. We found the best selection at Gifts for Professionals:
http://www.giftsforprofessionals.com/desk-accessories-frames-leather-picture-frames.html Having the photos with us reminds us that even though we love being on the cruise, we have precious beings waiting for us at home.
Have a great trip. Cheers, Fred