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Unlike most treats, popcorn sales actually rose during the Depression. Instead of installing indoor concession areas, theaters charged outside vendors a dollar a day to sell popcorn from outdoor stands. In 1938 Glen W. Dickson, the owner of several theaters throughout the Midwest, began installing popcorn machines in the lobbies of his theaters. The construction changes were costly, but he recovered his investment quickly and his profits skyrocketed. The trend spread quickly.

https://www.pbs.org/food/the-history-kitchen/popcorn-history/

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Overall, the proliferation of popcorn during the Great Depression is a good example of an inferior good that turned into a mainstay.