It depends on what you already have and what you like to photograph. What cruise are you taking, and what shore excursions are you planning? None of this information is in your original post. As a veteran of about 15 cruises, I suggest an ultra-wide for ship interiors, a wide-to-short telephoto for general purpose photography both on and off the ship, and a longer telephoto for ship details and any other object you want to zoom in on.
On a recent cruise, I took all five of the lenses in my signature, but never used the 10-22. In its place I used my Rokinon fisheye and de-fished its images when necessary. On my 70D I used mostly my 15-85, 8mm fisheye, and 70-300L. I used my 70-300L more than usual because my shore excursions included the San Diego Zoo.
I would take, in order of priority, my 15-85, 8mm fisheye (or 10-22), and 70-300L for my crop-sensor 70D. For pool-photograph and snorkeling, consider an underwater camera, such as my Olympus TG-2.


