Kodie: Yes, you can establish your account with your credit card and settle at the end of the cruise with cash.
I love my RCCL VISA credit card, which I use to secure my seapass. I've had mine since 4/03 and am about to qualify for our second free cruise. I get double points for any RCCL purchases, including, bookings, tips, excursons, bar tabs, CORKAGE fees (!), and any other RCCL purchases. It is so convenient to not to deal with cash. Also, regarding the RCCL credit card, to really get a free cruise (what we do is upgrade and pay the difference between outside cabin and suite-it worked out to a $2500 credit on our upcoming cruise), you must pay off the balance each month and not pay ANY interest. It takes discipline, but it's well worth it to do so.