Kevin Smith worked in the store where they shot the film. They shot for 21 straight nights. He would clock in at 6am and finish at 11pm. They would then shoot till 4am, after which he would try to grab an hour or two's sleep before getting ready to go back to work.
Kevin Smith, a keen comic book fan, sold a large part of his collection to help fund this film. He has since been able to buy most of them back.
Jason Reitman has said that this film inspired his desire to be a filmmaker. Reitman later told Kevin Smith this, which lead Smith to jokingly quip, "You're the son of Ivan Reitman. You grew up on the sets of Ghostbusters (1984), and Stripes (1981). It took ME to let you know that you can be a director?".
Clerks is loosely based on "The Divine Comedy" by Dante Alighieri hence the name of the protagonist, Dante Hicks. Also, there are nine breaks in the movie to represent the nine rings of hell.
Kevin Smith: [Star Wars] There are multiple conversations and references to the Star Wars films including, but not limited to, Randal's discussion about the end of Return of the Jedi and the song about Chewbacca.
Kevin Smith: [37] A recurring number in many of Kevin Smith's films, 37 originated in this film as the number of guys Dante's girlfriend, Veronica, has fellated.
Kevin Smith: [Jaws] (at around 1h 16 mins) After the fiasco involving Caitlin and the dead guy in the bathroom, Randal is pulling a chip through a jar of salsa saying "we're gonna need a bigger boat..." alluding to Jaws (1975), one of Smith's favorite movies.