CAMANO ISLAND — Customers can buy a 5-cent piece of gum from the bucket on the counter.

It’s the cheapest thing you can find at Cama Beach State Park’s old-timey store, or just about anywhere else these days. Customers, who are overwhelmingly children, snapped up 6,000 pieces last year.

For John Custer, one of the retiree volunteers who keeps the nonprofit store running, it’s about much more than sales.

“We like to think of it as 6,000 math lessons,” Custer said.

The Cama Beach Foundation started the store six years ago as a way to support free educational programs at the park. The only retail outfit at Cama Beach, the store is staffed seasonally by 14 volunteers, who work three-hour shifts as cashiers, stockers or pricers. The foundation draws from the island’s large pool of retirees.

They stock a bit of everything: snacks, drinks and fish bait, over-the-counter medicines, games and toys.

The store grosses about $30,000 each year, which pays for merchandise and store operations, with money left over for special programs.

Proceeds have paid for a college summer intern to work with the state parks interpreter specialist. The foundation bought an 8-inch telescope that an amateur astronomer uses for evening programs. The foundation is looking to enlist a second volunteer for the astronomy program.

They’ve hired a professional science educator to give twice-weekly programs for kids. The store helps support a weather station, low-tide beach walks and a “discovery wagon” full of skull replicas and pelts from local animals.

“It’s all hands-on, but it’s inquiry-based,” said Custer, a one-time high-school science teacher.

The general-store vibe complements the historic park. It occupies one of the original buildings from a private fishing resort built there in 1934 and operated by the Risk family until the resort closed in 1989. They sold it to the state parks system in the 1990s.

For the park’s inaugural year, in 2008, a concessionaire tried to run the store, but the business flopped, Custer said. It sat empty the following season.

Custer, along with friends Hi Bronson and Judi McDougall, got to thinking about putting it to use. Suzi Wong Swint soon joined the board of their new nonprofit.

“To tell you the truth, I had no idea whether this was going to work out or not,” Custer said.

The foundation is now an integral part of a volunteer corps that keeps Cama Beach lively and engaging for the young families who make up most of the park’s clientele.

“I have an 11-person staff — half of what I’m supposed to,” said Jeff Wheeler, who manages the island’s two state parks. “But because of the volunteers, this park thrives.”

More than 200 people have signed up for the park’s volunteer list. Custer credits Wheeler with making it easy to help out.

“Jeff goes out of his way to make this park work for volunteers,” he said.

Kari Lightner, of Camano Island, worked the store register on a recent Thursday as a swarm of children descended.

Lightner said she volunteers partly to keep her skills sharp from a career in retail. She’s getting plenty of practice.

Well before noon, she already had made 59 sales. The young customers looked to be 8 or 9 years old, on average.

“This is such a gorgeous place down here and it’s so much fun,” Lightner said. “This whole island runs on volunteers.”

Store hours are 10 a.m. to 4 p.m. daily from mid-June through Labor Day. It stays open Saturdays through the end of October and closes for the winter. It opens again Saturdays starting in April until the summer season is back in swing.

Noah Haglund: 425-339-3465; nhaglund@heraldnet.com. Twitter: @NWhaglund.