Cash in the casino- of course. You can get money on your credit card IF that is the one your account is getting charged to. I assume its the same on RCCL as Carnival in that you can get cash (with a 3 to 5% fee -CCL is 3%) in the casino using you Sign and Sail card (or whatever they call it on RCCL) So indirectly you are get cash with the credit card without having to pay cash advance rates/fees IF that credit card is the one on the sign and sail card.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013