David Carlson pondered the items in the glass case for a while before making his selection: a fossilized shark tooth.

The Edina 10-year-old, accompanied by his mother, took the $15 tooth to the register at the Explore Store at the Science Museum of Minnesota in downtown St. Paul and bought it with his own money. David, a shark enthusiast, said he would add the specimen to his collection of about 20 shark teeth.

“This one’s extinct, so I went with that,” David said. “They’re cool animals, and they’re not, like, really scary — they’re just like other creatures, except they need to find food.”

Win-win: a satisfying purchase for David, and mission accomplished for the Explore Store. Like most museum gift shops, it sells products intended to advance the mission of the museum itself.

“That’s kind of why we exist,” said Steve Fegley, the museum’s director of retail operations. “The gift shops at museums are typically extensions of the museums. Visitors can come to the shop and keep learning, even after their museum visit is done.”

Although many people consider a stop in the gift shop an essential part of a museum trip, some consider the shopping part a bit frivolous. After all, shopping is materialistic, whereas museums are educational. Shopping is about investing value and meaning in mere objects, whereas museums are about — oh, wait.

Come to think of it, buying an item in a gift shop and adding it to one’s own collection of possessions is a private echo of what the museum itself does on a large scale.

Most museum gift shops aim to offer merchandise related in some way to the museums that house them. So the shop at the Dorothy Molter museum in Ely, Minn., sells root beer made the way the famous one-time resident of the Boundary Waters Canoe Area Wilderness used to make it. The American Swedish Institute in Minneapolis sells products by Scandinavian artists. The Minneapolis Institute of Arts sells beautiful objects by artists from all over the world (including works specially crafted to celebrate the museum’s 100th anniversary). The Museum of Russian Art in Minneapolis sells nesting dolls, amber jewelry, Ukrainian eggs and lacquer boxes — including some museum-quality boxes priced at thousands of dollars.

“When they do a lacquer box, the very expensive ones, they use a single hair from a squirrel’s tail, dip it into paint and paint with a magnifying glass,” said store manager Michael Radcliff.

Museums “all have their unique identity,” said Christine Teel, retail manager and buyer at the Swedish Institute. “So you will see a really special assortment of products that make you say, ‘This isn’t something I would walk down the street and see at my local gift store.’ ”

Museum shops often contribute a substantial proportion of the institution’s overall revenues — a fact not just important to the museum but also to its customers, who like knowing that their money goes to a good cause.

“There are people who only want to shop in museum stores because they know the money goes back into the programming of the museum,” Teel said.

Government funding to museums is dwindling, leaving museums struggling to make ends meet, said Gloria Stern, store manager for Split Rock Lighthouse on the North Shore and treasurer of the National Museum Store Association.

Some museums, feeling the pinch, are succumbing to the allure of renting out the store space to concessionaires that sell similar mass-produced products in museums across the country. “I think they [the museums] are wooed by the idea of the steady paycheck,” Stern said. “However, it’s much more of a cookie-cutter way of running a store. They sell more mass-produced products, not as many local products.”

A national concessionaire might sell coffee mugs with a museum’s name on them but fewer individually chosen, locally crafted items.

Gift shop managers “are all very passionate about our museum and the products that we sell based on our educational mission,” Stern said. “A concessionaire does not have that passion.”