We have always used cash in the casino, and have a system we set up on every trip that works for us.
Before leaving home, we decide exactly how much we are willing to spend (meaning lose) on casino entertainment...because we really do believe its part of our entertainment and there is a 'cost' to that. The figure is for the WHOLE trip...and then we decide how many days are 'casino' days. (for example...when we went to Bermuda two years ago there were fewer 'casino' days because the ship was docked for 3 nights and the casino was closed...for our recent Freedom cruise we had seven casino days because the casino would be open every night)
Once we know how many days we'll make visits to the casino, we split the money evenly for those days and set up casino envelopes. That's our gambling money for the day...when its gone, its gone and we don't dip into any other cash.
Whatever money is left at the end of the day goes into the DONE envelope. Regardless of how much is left (more OR less than what we started with for that day) it gets put away and only comes back out at the end of the trip to pay off our on-board account.
We keep all the envelopes in the safe during the trip.
We cruised Freedom just a few weeks ago to the Western Caribbean. Seven envelopes of casino money...we finished EVERY night with money for the DONE envelope (probably 4 out of 5 nights with a little extra) and paid off the entire on-board account out of the DONE envelope with some to bring home.
May sound like a wacky system, but it works for us. We know exactly how much we are spending, keeps us from overspending and ensures we have the ability to spend time in the casino every day. Plus, we have ALWAYS had the attitude that we are in the casino to have fun, not win...and always expect to lose every dime of what we plan for the casino.