CHICAGO — Carolyn Marshall was headed to the gate for her American Airlines flight to California when she spotted the sleek tan machines with the neon sign across from Gate K6 at O'Hare International Airport.

She approached the side-by-side Farmer's Fridge vending machines, tapped the touchscreen menu and was hooked. The machines, stocked twice a day, sell salads in a jar, sandwiches and wraps, Greek yogurt with granola and other healthy fare. Marshall ordered an Asian chopped salad and a couple hard-boiled eggs for $12, swiped her card, and the items tumbled out, one by one, like a can of Coke and a candy bar.

"I love this idea,'' the Connecticut photographer said. "You're going to spend the money anyway, so you might as well eat something healthy.''

Airport vending machines long ago expanded beyond soda and snacks — what frequent flyer hasn't seen a Best Buy machine peddling Beats and Bose headphones and other name-brand electronics, or one of those pink, bus-shaped machines selling trendy Benefit Cosmetics?

But the number of machines and variety of items they dispense is on the rise as travelers embrace their convenience, airports love their limited real estate and 24-hour operation, and consumer brands use them as another outlet to serve existing customers and reach new ones.

Airports across the country expanding vending machine lineup

Las Vegas' McCarran International Airport added more than two dozen machines this spring, including four that sell decadent Sprinkles Cupcakes.

Dallas/Fort Worth International Airport is up to 15 machines, including two selling sundries from CVS, and is adding another one selling artsy Stance socks, a brand with more 1.3 million Instagram followers.

At New York's LaGuardia Airport, travelers passing through the newly renovated Terminal B are greeted with a row of vending machines selling Uniqlo puffer jackets, Sugarfina upscale candy and trial-size toiletry kits from Dollar Shave Club, a newcomer to airport vending.

Time-pressed travelers love self service

Gower Smith, the CEO of Swyft Inc., the automated retail technology company behind many brand name airport vending machines, said demand for new locations and new items for sale via vending machines is strong.

The company will soon add Pokemon vending machines at airports and also plans to expand into food and beverage vending machines. Smith would love to see Allbirds sneakers next to a Uniqlo vending machine some day.

"You're dealing with a savvy consumer these days,'' Smith said. "A self -service experience really hits a chord with them.''

Smith said he's bought a phone charger from a vending machine at San Francisco International Airport, Swyft's home base, and likely will pick up new Apple AirPods from a Best Buy machine instead of going to the store or ordering them online since the pricing is the same.

He likens the vending machines to bank ATMs.

"There's a time and place when you deal with a person. ... There's a time and place when you just want your cash out of the machine,'' he said. "We bring a choice to the consumer."

Scott Kichline, assistant aviation director in Las Vegas, remembers when the airport added vending machines selling iPods and other Apple products more than a decade ago — products the airport's retail shops didn't offer at the time. They brought in as much as $60,000 or $70,000 a month, he said.

Then there was the test of a Rosetta Stone vending machine peddling $500 software to travelers looking to learn a new language. Kichline and the airport's director sat across from the machine the day the test started and was "blown away'' when two kits were sold in 30 minutes.

"It's been a great format to test different products and things that are sort of nontraditional in airports,'' he said.

Vending machines never close and fit almost anywhere

One of the best things about having vending machines in an airport's retail and dining mix, airport officials and others say: they are always open.

The new pharmacy vending machines in Las Vegas, for example, offer toiletries, including toothbrushes. Those come in handy for stranded travelers when flight delays strike late at night and the airport news and gift shops are closed, Kichline said.

"It's kind of a great service to have,'' he said.

Farmer's Fridge, a Chicago-based company whose fridges are mainly in hospitals, universities, office buildings and drug stores, sees a lot of airport sales early in the morning and late at night.

"I don't know how many times I landed and everything's closed,'' founder and CEO Luke Saunders said. "It's a way to bring restaurant-quality food to travelers at odd times of the day.''

The vending machines are also popping up in areas where traditional airport retailers may not fit or don't want to operate.

Two of the Farmer's Fridge machines at O'Hare are in baggage claim.

In a parking garage at the Las Vegas airport, there's a MobileQubes machine renting portable phone charges. It was added last year next to the pickup area for ride sharing companies like Uber and Lyft, which are hailed via a mobile phone app. Chargers can be purchased or returned to another MobileQubes kiosk.

"People's phones were dying before pickup,'' Kichline said.

The Farmer's Fridge machines at O'Hare proved to be so popular with American Airlines employees on the go the airline put one in an employee break room.

American flight attendant Kim Hoover raves about the chopped salads. Last week, she stood in line for a Mediterranean salad with chicken in the K gates at O'Hare just before lunch time. But her salad wasn't for lunch. It was for dinner when she landed at the crew hotel at dinnertime.

5 things you didn't know about airport vending machines

1. There's an Instagram account for a Uniqlo puffer jacket bought from the Japanese retailer's vending machine at the Burbank, California, airport in March 2018. Angela Kinsey, who played accountant Angela on "The Office,'' sparked the "Angela's Vending Machine Jacket" account when she posted an Instagram video about the thrill of buying a $69.99 maroon ultra lightweight down jacket from the machine. The account has nearly 25,000 followers. Kinsey and her husband, actor Joshua Snyder, who have a YouTube baking channel, made vending machine jacket cookies in one episode after the story took off.

2. Ibuprofen is a top seller at CVS airport vending machines. The chain says it sells 12 times the amount of ibuprofen it sells at an average store. One of the busiest locations: the machine in Concourse A of Atlanta Hartsfield-Jackson International Airport. An estimated 25,000 people will use that machine this year. CVS has vending machines in 20 airports and is adding more each week, with San Francisco International Airport up next.

3. The four new Sprinkles Cupcake machines at McCarran International Airport have sold 6,000 cupcakes a month, at $5 apiece, since they were introduced earlier this year. The most popular flavor: red velvet. The least favorite: vanilla.

4. Good weather is better than bad weather for the grab-and-go salads and other healthy food at the Farmer's Fridge vending machines at Chicago's O'Hare International Airport. Lengthy flight delays and cancellations give travelers more time to sit down for a meal at the airport's restaurants, CEO Luke Saunders says.

5. The Dollar Shave Club vending machine at LaGuardia Airport in New York is the first airport vending machine for the subscription service. It opened in March.