if you ar planning on using a debit card check ahead of time with your bank, some have daily limits, often $500. this can pose a problem because you charge everything all at once at the end. call up your bank and they will raise it for you, although you may want to lower it again after the cruise for safety, in the event of a loss/theft
You can also settle with cash, or on the second to last day, just put cash on your account at the pursers desk if you feel you don't have enough in your debit account, avoiding your name called out before disembarking.
Meldrew of the Seas. I have tried it and no matter how I explain the advantages to the cruise ine, they would rather have cash or a credit card. I don't think they see the big picture...VBG.