Packing for a cruise is like packing for any resort-based vacation. You'll want to bring comfortable, casual clothing for daytime on board and in port, and swimsuits and workout clothes for pools, Jacuzzis, saunas and health clubs. To be prepared for dinner in the dining room, check out Dress Codes.
Think about the kind of shore excursions you plan to take and pack accessories, where appropriate, such as hiking boots, ponchos or rain gear, fleece jackets and snorkel gear. When traveling to tropical areas, such as in Central and South America, it's a good idea to carry insect repellent.
Pack all of your medications, prescription or otherwise, in a bag you can carry onto your flights. Obtain extra prescriptions from your physician for any medications you are currently taking and carry them with you.
Most ships have 110-volt outlets in every cabin, which will accommodate U.S.-built hairdryers, travel irons and electric shavers. Most new ships provide hairdryers as well.
Bring a hat, sunscreen and sunglasses for bright, sunny days on deck. You'll have many opportunities to have your picture taken by the ship's photographers, but you'll naturally want to bring your own camera or video camera as well.