The slot machines do take cash (or electronic withdrawal from your onboard account using your sail and sign card).
In my opinion, it would be cheaper to purchase a cruise than to try to get one off the casino points . Then again, I don't have a lot of luck there.
The Crown and Anchor Card is the sail and sign card. You will receive it when you board. It will be your room key, as well as your charge card on board. You cannot use cash on board (except in the casino) so all purchases are charged to your on board account.
On other lines you get one point for every three dollars that go through the machine (regardless of how much you win or lose).
If the line allows smoking in the casino (RCL does) then it is probably the only interior area that allows smoking. You will find many smokers lighting up, and the ships are not known for having great ventilation systems.
(Full disclosure - I have not been on an RCI ship, however the facts stated above are pretty universal. The casinos are not run by the ship, but by a contractor, so everything is pretty steady across the board)