Jay's costume is different in nearly every scene in the movie because the jacket he wore on the first day of shooting was his girlfriend's and he had a hard time borrowing it for the entire length of the shooting.
(at around 53 mins) When Dante and Randal leave the wake, it is still light outside, yet when they get back to the store, it's very dark outside.
Dante's beard changes because Kevin Smith asked Brian O'Halloran to shave his goatee before filming started during rehearsals, then, after seeing what it looked like without it, told him to grow it back. The scenes shot earlier in the shoot show a thinner beard while the ones shot last show a thicker goatee as it had longer to grow back.
(at around 35 mins) Disappearing "No Shoplifting" sign when Randal sells cigarettes to the little girl.
(at around 40 mins) Veronica says she'll see Dante at closing after dropping off the lasagna. After she says this, Dante makes the call to find out that the boss is in Vermont and he will be stuck there until closing. When Veronica had spoken to him, he was still expecting to leave for his hockey game.
(at around 1h 29 mins) In the closing credits, a character name includes the misspelling "maturbator."
In the "Thanks" credits, "Postens Funeral Parlor" is misspelled as "Parior."
(at around 1h 30 mins) In the end credits, the song title "Big Problems" is misspelled as "Big Poblem."
(at around 38 mins) During scenes of the VHS store close ups, specifically when the customer is viewing the Navy Seals (1990) box jacket; a VHS release of the movie Heavy Metal (1981) can be seen beside his right shoulder. Heavy Metal was not released until 1996 on VHS as legal difficulties surrounding the use of some songs in the film delayed its release to home media.
(at around 1h 12 mins) At the end of Caitlin's confrontation with Randal, Jeff Anderson momentarily breaks character and admires Lisa Spoonauer's butt as she walks away. (Kevin Smith points this out in the DVD/LD commentary.) However, due to Randal's sexual obsessions, this action was completely in character for him.
Throughout the movie, customers ask for cigarettes, but never mention a brand name.
(at around 27 mins) Randal mentions watching Star Wars: Episode VI - Return of the Jedi (1983) to Dante. However, the sounds coming from the TV in the previous scene are not from any of the Star Wars movies.
(at around 5 mins) The Chewlies rep's coffee cup is obviously empty when he picks it up to take a sip from it.
(at around 1h 21 mins) When Jay and Silent Bob enter the convenience store, and Jay is talking to Dante about how Veronica is a good girlfriend, when he says "I know she does a lot for you," his mouth doesn't move to the same phrase.
(at around 1h 26 mins) After the food fight, when Dante and Randal are sitting in the food and Randal is yelling at Dante while throwing candy bars at him, one of the candy bars does not make a sound when it hits Dante. Kevin Smith points this out in the 2004 commentary.
(at around 4 mins) At the start of the movie, towards the end of the song, Dante puts his head down on the counter. In the glass you can see Kevin Smith, the camera and the cameraman.
(at around 7 mins) In the beginning of the movie when we first meet Jay & Silent Bob the crew is briefly reflected in the windows.
In many shots towards the end of the movie, the camera and/or boom is/are reflected in the glass behind the counter.
(at around 15 mins) In the second shot of Willam The Idiot Boy (after Dante and Veronica stand up from behind the counter and sees Willam staring into space), the leg of a man can be seen moving quickly to the left-hand side of the screen. It is the clapperboard man, who didn't clear the shot fast enough.
(at around 1h) The official who hands Dante the summons claims that the charge can not be contested in a court of law. The Constitution guarantees that any matter involving at least $20 is eligible to be ruled on by a jury of the defendant's peers. Director Kevin Smith briefly acknowledges this in the commentary.
When Veronica chases the gum salesman and the customers, she says "Don't you have jobs to commute to?" She also is supposed to be in class all day. Later when Randal and Dante go to the wake, Randal says to Dante "It's 4 o'clock on a Saturday afternoon - how many people come to the store at four on a Saturday afternoon?" If it's a Saturday, how can there be classes all day, and why are the customers supposed to commute to their jobs? And we are told that the funeral is tomorrow which would be a Sunday. Funerals are not usually held on a Sunday.
(at around 1h) The Administer of Fines states that the little girl was sold cigarettes at 4 pm that afternoon. This is impossible because the sale occurred before the hockey game, which was at 2 pm, and Dante and Randal were at the wake at 4 pm. (The director admitted this in the DVD/LD commentary).
(at around 36 mins) After Randal sells the cigarettes to the little girl, Dante remarks that all the prices end in nine, yet all the price tags in the shot end in five.
(at around 9 mins) The gum representative buys some gum so he could claim to be a customer, however when he first went in, he bought a drink, so he was a customer anyway.