Take a suitcase full of suitable clothes, your personal toiletry items, and your wallet. Everything else you can get as you need it.

The other answer was rather vague (suitable clothes?) Casual clothes - shorts and tops or jeans for during the day, dressier at night. Women will want dressy pants, cocktail dress and possibly a formal for the Captain's dinner. Men would want to have a jacket and tie and possibly a tux or dinner jacket for the formal evening. Some cruises don't have the formal evening anymore, but some do. Usually the cruise brochure will give you some ideas. Don't forget your swimsuit and a light jacket in case it gets cool in the evening. Deck shoes for walking the deck and sightseeing on land. Dress shoes to go with your good dinner clothes. Don't forget your camera.

I'd like to add to postmuffin's respone: EXTREMELY comfortable shoes, as you'll be walking more than you'd expect. Casual, but not sloppy [maybe NEW] jeans are fine. You are less likely to be targeted as a 'tourist' in the stores in the ports you visit if you look more normal. ALSO- be sure and take anything like contact fluid, extra batteries, memory card, etc that will cost you an arm and a leg on board ship.

Alaska and postmuffin basically cover everything (especially with regards to batteries, etc - you'll need a mortgage to pay their prices on board) but I can add a bit more. When you book your cruise, you will receive a package in the mail with a book usually. This has luggage tags, tour information, what to take on board, what to expect, what documents to bring, etc. Look in that book first and foremost, as it lists a lot of good things (suit/dress, shoes, etc.) However, remember that you will be going to a foreign destination. Prices, exchange rates, etc. will be different. The quality of products will differ. Things you take for granted at home may not be readily available. If you need prescriptions, get them topped up (or a second batch depending on the length of your cruise), contact lenses, medications, and the like. I personally recommend buying one or two underwater cameras if you plan to do snorkelling or scuba diving. They cost $25USD on board, and I think $15 at home. Label your valuables (remember you will be with 2000+ strangers) clearly and don't go overboard - meaning, don't take every piece of camera equipment you have. Just take what you think you will need. I also recommend (depends on your habits) packing an empty suitcase. This may seem stupid, but when you see all the great deals on shore, you will be buying and buying. Then, when you need to pack it all up you will have little to no room. We normally pack 2 empty suitcases (one inside the other) and fill them up on a 7 day cruise. This all depends on where you go, for how long, etc etc. Hope this helps, Happy Cruising!

Sea sick tablets. Clothing that would be most comfortable to suit the climate you will spending your time in. (Casual and evening)

Follow your particular cruise lines guidelines for clothing. But the items I have not seen mentioned are a power strip and an air fresherner you can plug in and extra hangers and your own bottled water and soda pop. The power strip because there is only 1 outlet in most staterooms. The air freshner because lets face it you are surrounded by 2000 other people and it jsut helped. Extra hangers because there were only about 10 hangers provided. You can bring your own drinks aboard and avoid paying the hugh markups on the ships. We have sailed both Carnival and Royal Caribbean and this list applies to both cruise lines.

Sun block (or tanning lotion) and your lover

Besides the physical items that are necessary like comfortable shoes and clothing, toiletries, and medicines, also consider bringing a patient attitude (nee: island time attitude), spirit of adventure, and a healthy outlook for each day with a zest for living life. The Travel Slut®’s Tips on cruising: I do not consider myself an expert on cruising but I have cruised almost 50 times on at least 10 different cruiselines and I find cruising to be my favorite form of travel for several reasons. 1. Someone else drives 2. Someone else cooks 3. Someone else cleans 4. You only unpack once 5. You usually get 3-5 locations for the price of one and this is especially good when you are in an unfamiliar area and want to get a "taste" of what the area has to offer. 6. You can make many decisions or none at all--and you are always right 7. Being on or near water and sea air can be very calming 8. The likelihood of picking up a "bug" from unpure water or food is slim 9. You can experiment with new and perhaps unusual food, drinks and activities 10. Your travel budget is easier to manage. As a 1st time cruiser you will want to: 1. Study the ship to learn how to navigate between decks 2. Sign up early for things that require reservations (like dinner, tours, etc) 3. Find your "quiet-time spot"-whether it be the library, a secluded part of a deck, or even inside your cabin with the privacy sign displayed 4. Know how and where to muster in case of an emergency 5. Enjoy a verandah cabin at least once 6. Don't be afraid to ask any crew member a question you have. 7. Take time to relax--you don't have to "everything" that is available even though you may be tempted 8. Try new things and activities that you would normally not experience 9. Keep an open mind about weather (as you would for any travel) 10. Study your ports and if you decide to disembark, note the time the ship leaves port and be 30 minutes early and carry the name and phone number of each port's ship-contact person. Have fun!