But an increasing number are looking for the total shopping experience. The variety of things to buy is getting bigger and stranger - from foldable bicycles to bed frames. One Shanghai-based airline is even exploring selling real estate in-flight. That may not be too much of a stretch - some travellers already spend a small fortune. A passenger on a Cathay Pacific flight bound for Southeast Asia bought a Rolex Vintage watch priced at HK$195,000 in mid-2008.

In addition to the high rollers who surprise cabin crews every now and then with their big purchases, passengers in general have begun spending more since the negative sentiment from the financial crisis started to recede.

China Airlines, which operates 115 flights a day, had record in-flight sales of US$5 million in December, said Johnson Sun, the Taiwanese airline's Hong Kong general manager.

'People tend to spend more when they are on board, boosted by the holiday mood,' Sun said. 'It is a contrast to how price-sensitive they are when it comes to air fares.'

The two airlines - which operate more flights in and out of Hong Kong than any other carrier - say their in-flight sales have fully recovered even though receipts from ticket sales are still below those of 2007 because fares remain low.

Cathay's duty-free sales returned to pre-crisis levels in the final three months of last year. Sales in December were up 27 per cent year on year, a record monthly increase.

Perhaps surprisingly, the fewer passengers there are in the cabin the higher the sales, Tony Detter, Hong Kong managing director of the In-flight Sales Group, which supplies in-flight products to Asian carriers, says.

'The cabin crew may be overworked and find it difficult to devote as much time or attention to the service if the flight is full,' he told industry magazine Duty Free News International in August.

In-flight shopping has undergone a radical change from the days when you could only buy perfume and liquor. Passengers can now get off the plane with wardrobes full of designer wear ranging from Versace sunglasses and Mikimoto pearl pendants to Swiss watches.

And unconventional items such as the foldable bicycles and luggage cases are being offered (of course, passengers need to collect or arrange delivery of such purchases upon their return home).

The top-selling items are skin- care products, watches and electronic goods, said Jasmine Hui, Cathay Pacific's in-flight sales and logistics manager.

The Hong Kong-based airline has seen double-digit growth in in-flight shopping sales each year since 2004 thanks to the greater range of items it is selling and a more sophisticated marketing campaign.

Cathay has increased the range of goods it sells on board by 45 per cent, to 257 items, over that period, and the proportion of passengers making purchase of HK$4,000 or more has doubled, while the proportion making purchases totalling HK$1,000 or less has fallen by 10 per cent, Hui said.

China Airlines has seen the same upward trend, especially on its flights between Taiwan and the mainland. Deep-pocketed travellers from Shanghai, Guangzhou and Shenzhen buy big on board, especially white wine, Sun said.

Since the duration of flights across the Taiwan Strait is quite short - around an hour and a half - the airline has expanded the number of cabin crew by one per flight just to cater for in-flight sales.

'As a result, sales have gone up by 20 per cent on the direct [cross-strait] flights,' he said.

The duty-free craze has not extended to all airlines, however. Because of high fuel prices, chilled wine bottles and flacons of perfume are making way for paying passengers - with some carriers, including Air New Zealand, scrapping in-flight sales to reduce planes' weight and hence their fuel consumption.

Meanwhile, many airlines are searching for innovative ways to expand their in-flight retailing to the ground. One of the ideas is a home-delivery service. Carriers such as Cathay Pacific, China Airlines and Singapore Airlines will home-deliver bulky items.

A pre-ordering service - allowing passengers to buy before taking off - allows airlines to reduce the duty-free goods carried on board.

And it seems no product is out of bounds. Spring Airlines, a Shanghai-based budget airline is exploring selling property on board, despite some problems involving legal procedures and staff training.

'We are negotiating about the idea with some property developers,' Zhang Wuan, a spokesman for the carrier, confirmed.

Taking off again

Airlines have seen inflight sales rebound and are diversifying their offerings. One recently sold a Rolex watch for, in Hong Kong dollars,: $195,000

Spreading their wings

Airlines are selling a wider range of items in-flight. Since 2004, Cathay Pacific has increased the range of items it sells by: 45%