– For as long as she has been a bookstore owner, Gayle Shanks has been an advocate not just for books, but for what some sellers call "sideline" products, from pens to notepads to coffee mugs.

"I've spent an enormous part of my career as a bookseller trying to convince my fellow booksellers that gifts are an enhancement to their stores, a profitable one," said Shanks, who has helped run Changing Hands Bookstore in Tempe, Ariz., for more than 40 years. "I can't imagine a store without sidelines these days. They've finally learned!"

At this year's national publishing convention, BookExpo, the sideline part of the business will be a main attraction. BookExpo, which runs Wednesday to Friday, will feature such companies as Taza Chocolate, Calypso Cards and Streamline Inc. in an "UnBound" section at the Jacob Javits Convention Center.

Jenny Martin, event manager for BookExpo and for BookCon, the fan-based show which immediately follows BookExpo, said the "UnBound" exhibits and programs are meant to help booksellers "integrate merchandise in an effective way."

Nonbook items are standard for Amazon.com and other online sellers, but for physical stores the sideline market is also an established and important source of income. A Barnes & Noble store that opened recently in Rochester Hills, Mich., includes "an amazing selection of educational toys and games, family games and puzzles and curated gift items for avid readers," the superstore chain announced in March.

Oren Teicher, CEO of the American Booksellers Association, the trade group for independent stores, said nonbook products can account for 20% or more of overall sales.

Because most sideline merchandise, unlike books, doesn't have a listed price, sellers have more flexibility in how much to charge. With profit margins often tiny, sideline purchases can be the difference between making and losing money.

"It's an absolutely indispensable piece of the pie," Teicher told the Associated Press during a recent telephone interview. "The challenge is to make sure the store looks like a bookstore. The 20% of products you sell doesn't have to take up 20% of the space. It can take up 10% of the space."

Some stores blend books and sideline items right into their names, like Element of Fun Books & Toys, based in Rochester, N.Y.

At Changing Hands, customers can buy scarves, socks, garden accessories and pottery, part of Shanks' aim for her store to be "a one-stop shopping experience."

Warwick's in San Diego is divided into areas for books and nonbooks.

"I jokingly call us the 'everything store' because we do have cards, mailing supplies, filing folders and fine pens," said Adrian Newell, Warwick's' head books buyer and operations manager. "And the two sides complement each other. We know people who look for other things and then buy books, or regulars who come in, buy the newest book and then walk to the other side of the store and get a card."

For years, the power of the superstore chains Barnes & Noble and Borders and the emergence of Amazon led to dramatic shrinkage in the independent market and concerns that local stores might not survive.

But over the past decade, Borders has gone out of business and Barnes & Noble has scaled back amid ongoing financial struggles. Amazon's strength continues to grow, but the leveling off of e-book demand has stabilized the market for physical books.

Teicher said independent stores remain "fragile," vulnerable to higher rents, increases in the minimum wage and the continued growth of online retail.

Revenue from the 650-750 reporting stores are up about 1% in 2019, compared to the more than 5% increase in 2018 over the previous year.