If you're going to be using your credit card for your onboard charges be aware that they'll put a "hold" on your card for a certain amount. Also, be sure to call your credit card company(s) to tell them you'll be out of the country.
I'd take two cards if I were you. One for the onboard charges and another for onshore purchases.
I know some people take Traveler's Checks, but then you have to go to the Purser's Office to cash them which can be a pain if there's a long line.
Like danacline, we distribute our cash in different places in our luggage and on ourselves