The dog that ate the burrito after it was thrown onto the ground was not a trained dog, but a local stray. He simply walked into frame, took the burrito, and walked away. Both Marin and Chong ad-libbed around this, and it was left in the film.
Lou Adler screened the film privately for Jack Nicholson who had just been in a car accident and had a dislocated shoulder. It proved to be a painful experience for Nicholson, for his shoulder hurt him ever time he laughed - which was often.
The team found it hard to get any of the traditional advertising outlets to promote their film so they hit on the novel (and ultimately successful) idea of putting comic strips on bus benches. This gave the film a certain "street" feel, helping it to become a cult hit.
Chong's character's name is mentioned once at the beginning of the movie. He is referred to as "Anthony" by his parents. It is revealed in one of the deleted scenes on the DVD release of the film that his full name is Anthony Stoner.
An early lineup for the legendary LA punk band The Germs had auditioned for a part in the "Battle of the Bands" sequence for this film, along with a few other bands of the time. However, Darby Crash and the rest of The Germs instigated a food fight at the Roxy during their audition gig (in front of a live audience) and they were told that they would not be in the film. The other bands which auditioned were given time in the movie. The song The Germs played at the audition, "Sex Boy" (with sounds of the resulting riot) can be heard on the CD "Germs(MIA)".
The payphone that Pedro (Marin) is talking into in Mexico was a prop. The fake phone was supposed to be stuck onto the wall with double sided tape, but it kept falling down. Because of this, he had to speak with his hand on the prop to keep it from falling.
Near the end of the movie, Cheech says "We're gonna be bigger than Ruben & The Jets." This could be a reference to a doo-wop parody album recorded by Frank Zappa & The Mothers of Invention called "Cruising with Ruben & The Jets." Reportedly, the cover of the album confused many DJ's, and they thought Ruben & The Jets was the name of the band. Most likely, though, it was a reference to the (real) doo-wop band by the same name who formed after Zappa's album was released. They asked for his permission to use his fictitious band name, and not only did he agree, he produced the first album. Ruben and the Jets' singer, Ruben Guevara, appears in the film as Tom, one of the horn players in Cheech & Chong's band.
Strother Martin and Edie Adams (who played Arnold and Tempest Stoner, Anthony "Man" Stoner's parents) were allowed to ad-lib their dialogue in the scene where they talk to their son about getting a job.