Kevin Smith actually worked at the convenience store in Clerks. He worked all day, and they filmed all night (thus the closed shutters) for 21 straight days. He slept one hour a day during filming. The whole production cost $27k, funded by maxing out credit cards and selling his comic books. By the end of the 21-day shoot, Smith was unable to stay awake while some of the most climactic scenes of the film were shot.