The gift shop on the ship has the printed DCL paper and some kits as well. (Not sure if it is what is available on the store website or not?). It is pretty limited though. If you have a cricut or cameo you can do cuts of the characters and just cut their clothes out on tropical paper, etc. Enjoy your cruise, you will love it!!!
Here are the characters in front of the Disney Magic at Castaway Cay. I brought the 12x12 scrapbook papers along with some markers, dropped it off at the front desk on the day we boarded and on the last day, I got the papers back with all the characters signatures. I did have the black mat already on the sheet of paper when I got there so they could sign around it. I then purchased the stock photo at the photo gallery on board.