Do you know what kind of retail shopping is available on board? Think one of my first tasks upon boarding would be to hoard some bottled water and food items for a couple days and see what else is available for free and purchase. Since you're willing to burn through some money, buying overpriced (and heavy) batteries on board may make more sense than using your 50lb luggage allotment to carry a bunch.
I'd be more worried about some mechanical failure or virus that makes life on board unpleasant than I would be getting marooned on an island or the ship sinking.
But thanks to ETS I'll hardly walk around the block anymore without three means of making fire (Bic lighter, matches, firesteel), knife, whistle, button compass, flashlight/Petzl Zipka, cash.
Fortunately those items can fit in a single jacket pocket.
I think the notion of a manbag/duffel is wise since something could happen when you're away from your room. Being female I'm accustomed to lugging a purse or other shoulder bag everywhere and I surely would on a ship even if I were not crisis survival-minded.
This link below is to REI's lightweight (134 cu in.) "Flash 22" backpack. I have several of the smaller/lighter Flash 18s but for the ship would want the 22 for the water bottle holders. Think I'd keep something like this in my room for the Gilligan's Island gear (minus the fire/knife/button compass which will be in my shoulder bag).
http://www.rei.com/product/844631/rei-flash-22-packI'd also be looking at clothing options for pockets. I have some tropical-weight button-shirts (with SPF protection) that have great pockets.
You might also look at Tilley hats because they are great and all I have include a pocket at the top where I stash cash:
http://www.tilley.com/Hats-Men.aspxGood luck. Be sure to also plan for the 98% likelihood that the ship will sail smoothly, the toilets will flush and the a/c will hum throughout.
Meanwhile, I do enjoy these logistical planning exercises.
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