Being comfortable is a top priority during your cruise vacation -- casual wear is the standard daytime attire for most cruises. It's best to bring a variety of footwear choices including low-heeled shoes for walking on deck, sandals for beach excursions and a pair of dress shoes as well.
Many cruise lines include a couple of formal dinners, so check with your cruise counselor for details on appropriate attire.
You'll also want to think about the kind of shore excursions you want to participate in and pack accessories, where appropriate, such as hiking boots and binoculars. Depending on when you travel, you may also want to pack a sweater or light jacket for cooler nights.
Remember to pack all of your medications, prescription or otherwise, in a bag you can carry onto your flights. A hat, sunglasses and sunscreen are all necessities for sunny days on the ship.