I usually wear shorts and a tank top. Then hubby and I go back to the room to get our suits and sunscreen on to go out on the beach. But there are plenty of people who wear their suits and cover ups to breakfast.
My wife usually wears a tshirt or tank top with gym type shorts to breakfast and then we go change in the room before heading to the beach or pool. Trust me you will spend a LOT of time in your suits and the Jamaican climate doesn't really dry them that well so a damp suit (even from a day or 2 before) wouldn't be much fun to eat in enjoy your trip!!
I tend to wear a swimsuit with coverup - but we usually head straight to the beach after breakfast. Note at CSS your stomach has to be covered so if you have a bikini top on you need a coverup on top as well as bottom. I am not sure if that is required at all resorts (ever since I had to go change at CSS I have always just covered up).
I think the only requirement at the restaurants is that if you are wearing a swimsuit, that you have a coverup on and you must wear shoes. I see most people in either shorts & tee shirts or swimsuits and coverups. The same applies for lunch. At CN, if you go to the Beach Grill for lunch, you can go in your swimsuit without the coverup.