"Needless to say, I put it in my checked bag at the airport," Berger said. "A colleague who didn't got taken aside by security."

Cannabis-industry consultant Chris Jones was pleased when he was given a Hanu Stone vaporizer at a recent conference. Jones described the gift, which retails for around $50, as "one of the more advanced vape devices on the market." The website Engadget approvingly said it "hits like a ton of bricks."

All three were recipients of knickknacks formally called promotional products but better known as swag. The given-away pens, notepads, phone chargers, flash drives and water bottles clutter office desks everywhere. No conference or trade show is free of tote bags filled with stuff bearing company logos. The swag industry generates nearly $25 billion in annual sales and employs more than 130,000 salespeople.

"Swag is the only kind of advertising people thank you for," said Tim Andrews, chief executive of the Advertising Specialty Institute, the swag world's trade group.

Sensing opportunities that could make you feel like swaggering, Jeremy Parker and Josh Orbach teamed up almost four years ago to launch Swag.com. Today their Garment District–based company employs more than a dozen people and generates more than $6 million in annual revenue, which Parker projects will double next year. The firm has raised $2.8 million from investors, and its latest round was led by New York venture capital firm Uncommon Denominator.

"Every year swag grows," Parker said. "Even when the economy declines and marketing spending falls, companies still spend on swag. I think that's because they know their employees are nervous, so to make them feel better, they give them an $11 pair of socks."

Part of Swag.com's success is due to its sophisticated website, which Parker said makes it easy for customers to quickly pick the exact color and composition of whatever they're shopping for. The firm works with 30 "core vendors," including Liberty Print Co. of Beacon Falls, Conn., a certified woman- and LGBT-owned business that makes T-shirts in a former brass mill dating back to 1888.

"We definitely don't produce as many imprints as a lot of shops, because attention to detail is important to us," said co-owner Monica Maglaris.

Another reason Swag.com has caught on is its name, which somehow hadn't been claimed by anyone else in the swag space. The founders bought the handle from a domain squatter for $200,000.

"He wanted millions," Orbach said. "Negotiations took months."

Swag.com's first client was Facebook after Parker vowed his firm would undercut any competitor to win a $3,405 order for some T-shirts. Next the duo approached WeWork, whose executives asked whom else they had worked with.

"We said Facebook, and I guess they assumed we had other customers," Parker recalled. "They ordered $19,548 worth of T-shirts, each of which has Swag.com on the label."

Katherine Mayo, office manager at Blockchain in SoHo, said Swag.com's stuff helps build staff camaraderie, which is especially helpful for a company whose business of holding and trading cryptocurrencies for clients exists mainly as blips and bytes.

The hardest part with freebies is coming up with items that are cool but not so cool that someone would run off with them.

"If someone sees a backpack with our name, they might steal it, get the computer inside and unlock the crypto," said Mayo, who recently placed an order for duffel bags with Blockchain's logo fading into the background.