I have done quite a lot of cruises, many caribbean, alaska, panama canal, and more. I have tried all sorts of camera combos, from lugging on mulitple bodies, 5 lenses, tripods, monopods, flash's, ect, ect, ect.
My setup for my next cruise in the fall will be:
5D with 17-40 F4L
1DMKIII (or 7D if I buy one to save space) and my 70-300 IS L which I bought specifically for being compact for travel.
Maybe my 580EX, and I do find that a travel sized tripod can be good for a few things, but don't go overboard in that department since they are a pain to travel with. A lowlight prime is also a good idea for pictures in the ship of family ect, since the lighting is usually very low.
Over my cruises I have decided that having a kit that is easy enough to travel with will trump making sure you have every piece of the kit you might need with you.
I would also, depending on your itinerary, recommend getting some kind of a waterproof compact/helmet camera. In the past I have used a number of olpympus waterproof units, none of which survived for long, and now have a gopro hero HD 2 for the purpose. Some days you will not want to lug around your gear/you will be getting wet or doing something that just plain doesn't allow a heavy SLR. I mean I tend to do more "adventure" excusions than walking tours, like ATV's, zip lines, ect.
Most of the photos in this gallery were taken on cruises: http://www.pbase.com …raphy/landscape_&page=all