What you decide to bring on the cruise, depends entirely on yourself and the type of cruise you will be departing on. If you are going to warm beach destinations, you should take your swimming attire and light clothing. If you are travelling on a European River Cruise, you should bring more appropriate clothing for walking through city streets, and visiting tourist sights. You should also consider clothing appropriate for dining out in and attending live shows. Good footwear is recommended, as is headwear and sunglasses.
You should also consider bringing a camera, any toiletries, money / credit cards, and your passport.