I would think that ready cash in small bills would be your most important item.

Physical items to carry:

PERSONAL SANITATION/HYGIENE:
2 rolls of toilet paper in ziplock bags
2 traveller's packs of antibacterial wipes
A package or roll of small garbage bags

FOOD/WATER:
4 Mre's or 2 bx of your favorite Poptarts
1 package of "Fun Size" candy bars
Bottles of water stashed AFTER you get onboard (from ship'is stores)

MISCELLANEOUS:
50-60 ft of 550 Paracord
Multi tool
Sturdy metal soup spoon
A ball or boonie hat
A Doug Ritter PSK
Road Maps of the Ports of Call of your itenarary
Flashlight w/ spare set of batteries

INTEL/RECOMMENDATIONS:
Attend & be serious at the Lifeboat drill(s)
Know where lifejackets are stored in your cabin, lifeboat assigned, & in between
Designate a meeting place onboard in case of emergency, near your assigned lifeboat.
DO NOT get too familiar with crew members, maintain an invisible wall between you.
Research your Ports of Call. Know the Political and Economic situation in each. Know what the local Corruption Levels are. Know where the "Bad Areas" are and stay away from them. Know what can and CANNOT be photographed. Do NOT try to buy illegal items on the street.
Always practice the Buddy Plan. Stay with your group.

That's what comes to my mind. Good Luck and enjoy yourself.