On RCCL once you've cruised once you get a great coupon book in your cabin. It's free if you're a crown and anchor member(more than 1 cruise) and the booklets have really cool things like...
5 minutes free internet service
2 for 1 drinks at the bar
Free 5x7 photo
$5 casino chip
Lots of good stuff and a great way to value their recurring Customers!