Well, that's kind of the problem, but also what we are working on and hoping will work. After the family emergency, we were left with about $200. We've managed to scrape up another $100 from some other accounts. That will cover fuel/food just for the drive there.
What worried us was that we wouldn't have any money for the first day (and subsequently was worried that they wouldn't even let us board as a result). Anyway, my wife has a business transaction today that should give us an extra $200-300 and we've decided to pawn our iPods, which should give us another $100-200. That should easily give us enough cash to put down for the first day and then switch to the debit card the next day when the money hits the bank.
That should close our case, but I'm still curious what would happen if you were to show up to the boat absolutely empty handed (but with the all-inclusive cruise itself 100% paid for, of course): no cash, no credit, nothing but your luggage (stupid, I know, but play along with me). Would they let you board and simply disable any charging abilities or would they turn you away?