Here's a fact that probably won't surprise many people.
Flights to Las Vegas make the most money selling beverages of all domestic routes.
"Alcohol sales on the way to Vegas are higher for sure than on the way back from Vegas," said Brett Proud, CEO of GuestLogix, a Canadian firm that tracks what millions of people buy when flying.
In the first half of this year, six airlines in North America tracked by GuestLogix made 58 percent of their onboard revenue by selling beverages, 38 percent came from food sales and 4 percent from the sale of passenger comfort items like headphones and movies.
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Frequent flier Evan Sears isn't surprised the average flight to Vegas made $109.70 off of beverage sales. "I was on a flight to Vegas just last week, there were a lot of people getting it going early."
Longer flights, more money
CNBC asked GuestLogix to analyze more than 2 million in-flight transactions from the first half of this year. One trend stands out: The longer the flight, the more we spend.
"On flights with duration of 2½ hours, we're seeing more and more folks open up a tab onboard," said Proud.
That's one advantage of more airlines going cashless and requiring customers to pay for drinks, food and movies through a credit card.
So what routes in the U.S. bring in the most money for drinks?
Each route features flights longer than 2½ hours.
More passengers buying; big Thursdays
After tracking millions of in-flight transactions, GuestLogix has gained an insight into what and when travelers are buying on board.
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Among its findings:
Twelve percent of passengers in 2013 will make at least one on-board purchase while flying—four years ago it was 7 percent. Drink sales are greatest on Thursdays. Proud noted this could be due to the fact many people are heading home from business trips and are more likely to unwind with a drink. The day after a holiday is slowest for sales.
Passenger comfort sales are up 19 percent this year. This is the area where airlines are seeing the biggest growth.
Flying retail centers?
Proud said the combination of passengers becoming more comfortable buying on flights with credit cards and airlines looking to grow revenue from a captive audience means even more will be sold in flight.
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"There is still a merchandising opportunity that's out there, far beyond just offering duty-free products," said Proud. "That will help airlines save on fuel, but it also means they can offer lots of different things and ship products to folks' home addresses."
But not everyone thinks the airlines can turn their planes into flying retail centers. Aviation consultant Michael Boyd said there is a limit to what passengers are willing to buy.
"Unless it is directly product related it is not going to sell. People aren't going to buy things there," explained Boyd. "To think that people are going to buy normal things on an airplane that they don't need for their trip just isn't going to happen."
—By CNBC's Phil LeBeau. Follow him on Twitter: @Lebeaucarnews.