1. Plastic baggies to pack a lunch for port days
2. Camel back or hydration pack to fill with water for port days. My backpack has this built in with a straw over my shoulder to access water.
3. Bright color luggage tags to identify your luggage especially if you have black luggage. Their is nothing worse than looking at the name tags on 100 pieces of luggage to find your own.
4. Small bills for tipping luggage handlers before boarding