Check out your cruise ship's website. Many cruise ships will have suggested attire for dinner on certain nights. The suggested dinner attire may be casual, smart casual, and formal. Casual means slacks, sport coats, and sundresses. Smart casual means jackets with ties and nice dresses. Formal means suits with ties or tuxedos and cocktail dresses. Sometimes you can rent tuxedos from the cruise ship. Usually the formal nights will be on nights when you spend the day at sea or if there is a holiday, such as Valentine's Day. Keep in mind that this is suggested attire - many people pack clothing that is dressed down a little from what is suggested, especially if they do not own clothing that formal. You will usually be fine in whatever you wear to dinner, unless it is a bathing suit, shorts, or T-shirt. If you do not want to dress up for dinner, there is usually a casual dining restaurant that does not have suggested dress up attire.
You will probably swim in the pool or ocean on your cruise vacation, so you will need to pack a swimsuit and flip flops. Since you will be swimming probably every day, and it takes at least 24 hours for a swimsuit to dry, I would suggest packing 2 or more swimsuits. Make sure to pack some hand washable soap, such as Woolite, to wash out your swimsuit in the sink and hang dry.
Depending on your cruise excursions, you may need long pants or jeans. You may be riding horses or going on an ATV. Both of these activities require, or suggest, long pants or jeans. You may get dirty or muddy on these excursions, so you may want to pack more than one pair of long pants or jeans if you can't wash and dry them in enough time before they are needed again.
You may need good quality walking shoes for your cruise. If you are going on a long walk or hiking through the jungle, you will need quality walking shoes. You may get muddy if you go on a hike, so pack more than one pair of walking shoes for your cruise.
You may want to pack workout clothes if you want to work out at the gym or play sports during your cruise. If you plan on doing this everyday, you may want to pack more than one set of workout clothes if you can't wash and dry them in enough time before they are needed again.
You usually do not get access to your baggage for several hours after boarding the cruise ship, so make sure you pack everything you might need for the first 6 hours in your carry on bag, such as your swimsuit and flip flops.
Make sure you check the temperature of the ports you will be visiting during your cruise online before you go. The ports may be much cooler or much warmer than you expect. Make sure to pack a light jacket, even if you don't think you will need it. A rain poncho is another good thing to pack.
