Me and the misses got back from a cruise in April. I took along my maxpedition colossus and carried with me the following items:
SAK-deluxe tinkerer (20 bucks at the local Wal-Mart, if I have to ditch it, no heart breaks)
Purell hand sanitizer (2oz)
2 Dozen ez-wipes (individual packages)
Sunscreen, both spray on and creme (misses is very fair skinned and burns easily)
Bottle of Advil (small size)
Bottle of pepto (4oz I think)
Small sewing kit (Raines military sewing kit)
Inova XO led light
Doug Ritter's designed PSK (overkill maybe, but weighs practically nothing and if I go overboard with out the vest I have a whistle and signal mirror)
One set of spare batteries for everything
That's basically what comes to mind, fair warning.....check the local laws concerning knives where you go. I went to the Bahamas, which being a British Commonwealth meant sub 3" knives that could not lock, so my swiss army knife was ok. In Mexico knives are not allowed. Period. I found it wise to put the SAK on my keychain for the cruise-right out in the open so they could flag it right off the bat if they wanted to. Figured it was easier to hoof it back to the truck if need be rather than have to ditch it.

-Bill Liptak