Winston Aldworth: I'll have what she's having

Researchers found that air passengers are 30 per cent more likely to make an in-flight purchase if the person sitting next to them makes one first. Photo / iStock

On a Jetstar flight a couple of weeks back, I asked a flight attendant for a cup of water. Which is pretty much the only thing you'll get for free on a low-cost carrier.

The staff member was moving from the front of the cabin towards the back and no one ahead of me - at least, no one that I'd seen - had asked for a drink of water (I know, I'm such a rebel, right?). After I asked for water, a whole lot of people behind me did the same thing.

None of which would be worth commenting on, if not for the fact that it underlines a psychological trend that can cost you money.

Researchers at Stanford University found that air passengers are 30 per cent more likely to make an in-flight purchase if the person sitting next to them makes one first. Meaning, you hadn't planned on buying snacks, but when your neighbour hands over a couple of bucks and tucks into a packet of chips, a faceful of salt 'n' vinegar suddenly seems like a good idea.

With the low-cost model soaring, ancillary revenue - the cash airlines make from food, drink, entertainment packages and upgrades - has become big business. Globally, airlines made $46.5 billion from ancillary sales in 2013.

And the powers of suggestion and peer pressure are playing their part.

We should trust Stanford University on the subject of psychology aboard low-cost airline carriers - the university's most famous study is the notorious Stanford prison experiment.

So the next time you see someone on a plane buying a packet of chips, fight the urge.