There are several choices. If you just want to carry your S&S card, wear something with pockets! Or you can have a hole punched in your card onboard and wear it around your neck or on your wrist with a lanyard.
If you want to carry your S&S card, some cash, a credit card, and a copy of your passport, etc., there are waterproof (around the neck) wallets in the fishing supply area of WalMart.
There's also a plastic around the neck container sold on board that will hold a little more "stuff".
Surprisingly, (or maybe not) , you can also find one of these for free with the purchase of a certain brand of rum at your liquor store!
Have a wonderful cruise! Wish my clock was a short as yours!