They provide flyers FREE (yes, FREE) tickets on their flights. They make money on baggage check, selling peanuts, etc.

I would assume most of their business is cash-based.

Why not offer a "debit card" at the beginning of your flight that is tied to your credit card? The card would be akin to the hotel room key you are given at checkin -- tossable yet reusable. Heck, to make some more money, throw advertisements on the cards like Holiday Inn does.

You use this "debit card" to check in, buy in-flight entertainment/food/drinks, etc. Basically you can go through a bunch of micro-payments during your flight. You may even have to pay to use the potty, and this again would be a great use of the card.

As soon as your flight lands, the "debit card" expires, and the backend systems aggregates your charges and makes a single charge to your credit card, while emailing you an itemized statement of the charges during your flight.

Drives revenue, eliminates the need for handling cash and making change, and allows for inventory control, because everything is in the system. Sure, you may need a little reader/computer/wireless in every plane, but the savings and earnings from additional revenue would offset it quickly.

Maybe if RyanAir reads this and uses it, they'll give me Free airfare anywhere they fly! Oh wait...