Packing for a ship is packing for several trips at once: deck, dinner, port and party. Fortunately a small bag covers all four if you choose carefully.
Pack for layers
Decks are breezy even in the tropics. A light jacket and one warm layer cost almost nothing to bring and are often the most used items.
Shoes matter most
Comfortable shoes for ports, something dressier for evenings and flip-flops for the deck. Three pairs is plenty.
Bring the small things
A reusable water bottle, motion-sickness remedies, a waterproof phone pouch and a short charging cable. Check the ship’s rules before packing a power strip, because many forbid them.
Check your event’s dress notes
Themed events often have costume nights. Your host will say what to expect, so read the listing before you pack.