Lie in the sun (unless it's raining or too windy or your pale skin can't handle too much sun).
Go to a show.
Make small talk with people you will never see again (although you may become Facebook friends).
Watch TV in your stateroom.
One thing I can say for sure. When we pull into Miami tomorrow morning, this ship is going to weigh a lot more than it did when we left last week. Many passengers are planning the diet they'll start when they get home. Others will head right for Old Country Buffet.