I would say don't overpack. I always seem to do this. You'll be in swimsuits most of the day. There is no need for a lot of clothes. Also, be sure to wear your sunscreen and keep reapplying. The Jamaica sun is strong. I hate to see people on vacation that look like lobsters because they forgot to reapply. Also, just relax and go with the flow. Don't plan too much. :O)
Don't plan too much, sit back and relax. You will be in a bathing suit most of the day so don't take a lot other clothes. You can dress up at night if you like or not. You see a lot of both. This place is really laid back. There is no stress. Do what you want to do. Be excited. CN is a magical place!
Swim suits are the dress choice during the day, If you plan on going to the nicer restaurants women usually have on a dress or skirt guys will need slacks and a shirt with a collar closed toed shoes.
A must do is the cat cruise!! Its funny to see most people quietly talking or saying hi to each other when the boat first goes out and when it comes back Its like 50 family members laughing and dancing having a great time!!
Also Rick's Cafe is a must do, bring some cash if you go. Its gotten touristy. The most beautiful sunset in the world though. Check at the desk for the times a bus takes you. We took a cab at an earlier time once to get a table up on the point and have some drinks and watch the sunset.
If you've ever wanted to try scuba diving ask when Sugar (aka Karl) is instructing. All the instructors are very good, but we had a blast with Sugar.
The jet ski guys can be talked down on price, they always start crazy high be polite about it and they'll come down.
Other than that a massage and crashing on the beach are the other must do's. Ask the bartenders to surprise you and you'll get a great drink. Miami vice's and hummingbirds are popular so are the vodka lemonade slushy!!
There is a Restaurant at the Resort that requires you to be dressed up. If you plan on eating there, make sure you pack a nice shirt, dressy slacks and a pair of close-toed shoes and for your wife a pretty dress or skirt. They will not let you in wearing anything else, trust me I only know from experience. My husband and I were there last May for our Honeymoon and of course my wonderful husband forgot to pack any slacks or close-toad shoes. We were going to buy some slacks during our shopping trip, but no luck with shoes. So, needless to say we didnt make it to the fancy restaurant (bummer). Anyways, other than that I'd say dont overpack as everyone has stated in the comments...most of the tine you'll have your swimwear on. ENJOY!!
If you plan on scuba diving keep in mind that you can't do it within 24 hours of flying. We weren't aware of this on our trip to CSA last year and tried to late to book it and it was also filled up. So on our trip to CN this year one of the first things we're going to do is head to the watersports hut to line it up for mid trip.