Thanks for the suggestions so far. The cruise is for 7 nights in August and goes from Ft Lauderdale to several Caribbean islands which means it will be warm water. We are driving to Ft Lauderdale so no airline restrictions to worry about. We will have a room with a balcony which will allow us to dispose of biodegradable waste bags if forced to plus it provides light and fresh air and hopefully we won't have to sleep on deck if there's a power failure which I hear is miserable and wet.

I think I'm going to go with a small duffel bag with a shoulder strap instead of a backpack because that won't interfere with a life preserver and I can access the bag without dismounting it like I would have to do with a backpack. I think I definitely want to have everything in dry sacks inside the duffel bag for both flotation and water resistance as well as organization. Perhaps a small red dry sack for first aid, a small yellow dry sack for electronics, etc.

I already own a waterproof sat phone with GPS and ResQLink+ PLB. I am going to get the Katadyn desalinator and then gift it to my Dad who has a small saltwater fishing boat.

I've broken down things into the following areas:

sanitation - biodegradable toilet bags, wet wipes, hand sanitizer, rubbing alcohol, nitrile gloves
health - first aid kit, common meds, zinc oxide, sunscreen, small amount of toiletries (in case we are dumped on an island without luggage), Vick's for under the nose smell prevention if the toilets backup
smoke - Safe Escape ASE60 60 minute smoke evac hood
signaling/comms - sat phone, extra minutes, roll-up solar panel, power cords, PLB, mirror, whistle, strobe, two GMRS radios for talking around the ship, charger base, Radio Shack scanner (to monitor ship's crew comms), am/fm radio, cell phone, list of ship's frequencies
water - Katadyn Survivor desalinator, 32oz stainless water bottle, plastic water bottle, collapsible bucket, 100' paracord, Aquamira filter, chlorine dioxide tablets
clothing - Merino wool long johns tops and bottoms, lightweight shoes, hat with strap, lightweight windbreaker/rain jacket, mylar blanket
lighting - waterproof headlamp and small waterproof flashlight, extra batteries
food - Datrex 2400 calorie bars 4 bars per person, snacks, nuts, candy, drink mixes
money - several 1/10oz gold coins, $800 emergency cash, extra credit cards
papers - passport, list of phone numbers, travel insurance docs, map of islands
miscellaneous - lighter, boat matches, duct tape, ziplock bags, deck of cards, pipe tobacco, SAK with can opener, multi-tool, notebook, pen
fishing - hobo hand fishing rig with 1,000ft of line and a few hooks and lures. Might as well go fishing if the ship goes adrift with no power

Most items above with be x2 since it will be my girlfriend and I. We will each have a duffel bag and split up some of the expensive items like the sat phone, scanner, and desalinator between us. Some items like cash and sat phone we'll carry all the time but some items we'll dump in the room so we're not lugging a ton of stuff around the ship all day.

I still haven't figured out what to do about coffee. If they don't have hot coffee on the ship - now that would be a real disaster.

Any more suggestions would be greatly appreciated!