Be sure you have plenty of memory for your digital camera! Everything is so beautiful and exciting that you will want to take hundreds of pictures.
We have rain ponchos that have come in handy several times. You can buy them at a dollar store and they fit into quart-sized baggies. When we go on certain land excursions I take a canvas backpack and place stuff in that like the ponchos, camera memory, medications, sunscreen, anti-bacterial hand cleaner, island information, etc. It is lightweight and so handy!
Before our last cruise, I read in this forum about buying one of those shoe bags that hang over the door. I bought one for a dollar at the Dollar Tree and it was great. It is going on all of our future cruises. It is mesh and doesn't take up any room in the luggage. I hung it on the clothing hooks on the back of the bathroom door and it held most of our toiletries, keeping the limited counter space free of clutter.