Traditionally, the only things you've been able to buy in-flight are food and cocktails. However, with airlines expanding into the sales of items like blankets, cigarettes, and now WiFi, the door has been cracked for other retailing opportunities on board. American Airlines has reportedly broken the seal and is selling Heathrow Express train tickets on a limited basis for some LON-bound flights. This is a smart idea -- a win-win for the passengers and the airline.

Passengers gets to purchase train tickets without waiting in line or even getting out of their seat, while the cash-starved airlines get to pocket a little cash by doing a sales work for the Heathrow Express. This seems to be the kick-off of a real trend in air retail therapy, as several airlines report they too are cooking up similar deals. The most obvious hits are travel-related services: train tickets, metro tickets, theater tickets, shuttle bus vouchers, and the like. With airlines that already employ touch screens, like Virgin America, you wouldn't even need to really staff the sales, as travelers could click to buy on the screen in front of them. Certainly seems preferable to the pay-per-pee model, though that brought new meaning to the phrase "revenue stream."