Nothing is worse than snorkeling for hours on the first day of your vacation and spending the rest of your precious days in paradise dealing with a very sunburned back. What you need to pack for your sunny, swimmy vacation is a rash guard.
You may be saying to yourself "Fit, I am not worried about a rash. It is a sunburn I am trying to avoid." To this I will say, lightweight rash guards are made from fabrics with high UPF (Ultraviolet Protection Factor) factors, to keep your skin extra protected for long hours in the water. They are like a sunscreen swimsuit for your upper body.
Originally developed for surfers to prevent rashes from the sand and surf wax combo, rash guards are designed to move and swim in making them a much better option than swimming in an old tee shirt. Obviously they provide much better sun protection and this one, designed by O'Neill has a UPF rating of 50 plus. It even has a utility pocket with a drain hole - they think of everything.
Buy one directly from O'Neill for $49.95. Rash guards come in both short and long sleeve styles so your forearms can stay protected too.