I did a Caribbean cruise out of New York a couple of years ago. What I really liked doing is putting on my coat, taking a lounge chair on an outdoor deck, and sitting there to read, watch the ocean, and contemplate life for a while. It's brisk and invigorating, not crowded, and the freshest air you'll ever breathe.
It's also fun to take a sweatshirt and do some power walking around the deck. Before you know it, you'll be in warmer weather.