If going outside of the U.S., I would take a passport if you have one. We just lock it up in the room safe. We just got off a cruise where one passenger broke her ankle and had to leave the ship in Cartagena, Columbia and fly home from there after her surgery. I'm sure it would be more difficult in that situation if you didn't have your passport with you. We also had someone airlifted by helicopter off the ship when we were off the coast of Mexico (not sure where they took him exactly--it was the middle of the night). We have never needed our passport while on a cruise (after we use it to get on the ship), but you never know what may happen!