Holes

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Teenager Stanley Yelnats IV lives in Texas with his destitute family, who have been cursed with misfortune for centuries. His ancestor Elya broke a promise to fortune teller Madame Zeroni. The family had potential for a greater livelihood until Stanley's great grandfather was robbed by Katherine "Kissin' Kate" Barlow, a schoolteacher-turned-criminal. One day, Stanley is falsely accused of stealing a pair of sneakers and is convicted. He decides to attend Camp Green Lake, a juvenile detention camp, in lieu of serving a jail sentence.
He arrives to find that the camp is situated on a dried-up lake. The camp is run by its warden, Louise Walker, her assistant Mr. Sir, and camp counsellor Dr. Kiowa Pendanski. The inmates spend each day digging holes in the lakebed to "build character," and may earn a day off if they find anything interesting or unusual. Stanley is eventually accepted into his tent group and is given the nickname "Caveman" by them. Later, Stanley finds a golden lipstick tube in his hole with the initials "KB" engraved on it. He gives the tube to his group's leader X-Ray, who in turn gets a day off. On Walker's orders, the group enlarges the hole which X-Ray had dug, but they find nothing and eventually resume digging individual holes. Later, after taking responsibility for fellow group member Magnet stealing Mr. Sir's sunflower seeds, Stanley is taken to Walker's house where old wanted posters and newspapers lead him to suspect that "K.B." stands for Kate Barlow.
In a series of flashbacks, Camp Green Lake is a flourishing lakeside community in 1888. Kate falls in love with an African American onion seller named Sam, who helps rebuild Kate's schoolhouse. When Charles "Trout" Walker, the town's wealthiest man whose advances are rejected by Kate, becomes jealous of Kate and Sam's relationship, he destroys the schoolhouse and Sam's onion stand. Kate seeks the help of the town's sheriff, who is drunk in preparation for Sam's public hanging. He demands a kiss, but she refuses. Attempting to escape, Sam is killed by Charles. In response, Kate kills the sheriff and leaves a lipstick imprint on his cheek. As Kate commits robberies of local banks and stagecoaches, Green Lake dries up and the town is abandoned. In 1908, the now-bankrupt Walkers track down Kate and attempt to force her into revealing the buried treasure's location, but Kate refuses and tells them to dig for the treasure. A yellow-spotted lizard bites Kate and as she dies, she taunts the Walkers to "start digging". For the next century, the Walkers unsuccessfully dig for the treasure.
In the present, Zigzag fights Stanley out of jealousy when he realizes that in exchange for reading and writing lessons, Stanley's friend Hector "Zero" Zeroni assists Stanley in digging holes. Pendanski mocks Zero, but he attacks Pendanski and runs off. Stanley later finds Zero, who survives by using Sam's sunken boat as shelter and Kate's peaches for nourishment. When Zero refuses to return to the camp, Stanley discovers a mountain called "Gods Thumb" in the distance and remembers how his great-grandfather survived in the desert by climbing that mountain after Kate left him for dead. Stanley helps carry an ill Zero up God's Thumb, where they find a wild field of onions which actually belonged to Sam, and a nearby spring, regaining their strength and unknowingly fulfilling his ancestor's vow to Zero's ancestor to carry a Zeroni family member up the mountain, breaking the curse and restoring his family's luck. Meanwhile, his father discovers that peaches and onions remove foot odor, something he has spent years trying to solve.
On the mountain, Zero reveals that he stole the sneakers which led to Stanley's capture. Vowing to dig one final hole, Stanley and Zero return to the camp and investigate the hole where Stanley found the lipstick tube. They eventually uncover a chest, but are discovered by Walker and Mr. Sir. After they escape from Walker with the help of some of the yellow-spotted lizards, it is revealed that Walker is Charles's granddaughter, and she has had the inmates digging holes for several years in order to search for the treasure she believes belongs to Charles. The next morning, the Texas attorney general and Stanley's lawyer arrive, and the chest Stanley found is revealed to have belonged to his great-grandfather. Walker; Mr. Sir, who is revealed to be a paroled criminal named Marion Sevillo; and Kiowa Pendanski, who is a criminal impersonating a doctor; are captured. Stanley and Zero are released and rain returns to Green Lake for the first time in over 100 years. The Yelnats family claims ownership of the chest which contains jewels, old money, deeds and promissory notes which they evenly share with Zero. Zero reunites with his missing mother, Camp Green Lake is closed, and the Yelnats and the Zeronis move to new neighboring houses.

Question: What does Sam sell?
Answer: onions