I'll be wearing loose-fitting shorts and trunks with generous pockets when I'm on the cruise. Occasionally I'll be wearing khaki slacks, but no jeans or pocketless trunks. The Nikon J/V series might be too thick, even with a pancake, and I like zooming.
I'm pretty much set on just picking up the S100 and buying a waterproof bag for the beach. I wasn't planning any underwater shots or anything, but it will be around water a lot.
If I can afford the Sony RX100 by the time our trip leaves (one month) I'll get it, but I seriously doubt I'm going to do that.
My Nikon D7000 is coming with me and will be used for Puerto Rico walking tours and a few land-based excursions that are short and close to the boat. But for longer trips and around the ship I'll be using the S-100 most of the time.
Another option I might do is the SX150/SX160 IS. I had the SX110 IS and have nothing but praise for it. Sure, it's a bit thicker, but they are so inexpensive, take AA batteries (and can get hundreds of shots using Sanyo Eneloops), have a great zoom and IS combination, etc. Plus they have TV mode, which is good for waterslides, and other action-based events in which you can focus ahead of time and wait for the subject to appear.
Thanks for all the advice, everyone.