On the cruises that I have been on the ship will make a copy of a credit card or will want you to put money into an account.
Your statement is available every day at the pursers desk. The only draw back is you have to wait in line to get it. Some ships now have it available on the tube in your room. They will put a final statement in your room during the last night.
Save all of the slips that you sign so you can compare them to your statement.
Some ships also add in their automatic TIP that amounts to around $10.00 per day per passenger. So the minimun amount of TIP for you and your traveling partner will be $140.00 for a seven day cruise. If it is not automatic be sure to reserve about the same amount to give to the waiter, busboy and steward at the end of the cruise. If you are taking $1000.00 you will now have $860.00 to spend on gambling, drinks, excursions, shipboard shopping, etc.
Have fun and take a credit card just in case.