Both flights and in-flight purchases are now commonplace in ordinary people’s lives, so it’s time to start looking for new ways to pay.

Thanks to the interest in payments bitcoin has given me, I’ve spent more time observing how they’re handled in unusual environments — particularly airplanes.

Airlines love to sell stuff to their captive audiences. Booze, duty-free and extras — someone even told me about a Chinese airline that had a live salesman standing at the front, pitching products into a microphone for most of the flight.

In-flight purchases have been common for decades. With the rise of low-cost carriers (LCCs) worldwide such purchases have increased exponentially, as those airlines charge for all onboard services including meals, all drinks, and access to the entertainment system.

You see so much in-flight commerce today it resembles a mile-high cafe, or mall.

How are you supposed to pay?

Once upon a time, some airlines accepted cash payments in-flight — generally for domestic only. Staff described it as a painful experience, juggling change in narrow aircraft aisles and customers paying with large bills.

Given the number of different passports traveling on a typical international flight, the thought of all those people trying to use their national currencies in cash sounds farcical. Airlines who accept cash usually choose one currency per flight and, if it isn’t the one you’re carrying, tough.

As of 2009, All US carriers have been cashless. Virgin America was always so.

As a result of physical cash hassles, most cabins worldwide are now credit-card only, or offer a direct-debit payment system from customer bank accounts. The latter isn’t an option for those who don’t have bank accounts in that country.

Some LCCs also have a voucher system, where passengers choose the optional paid services they want before embarking, and hand over the vouchers once in the air.