Due to the low budget, George Lucas was unable to pay all of the crew members. He offered to give many of them a screen credit in lieu of payment, and they accepted. Traditionally, only department heads received screen credit. Giving screen credit to all crew members is now standard, which is why closing credits last so much longer now.
When Wolfman Jack makes an on-air prank call to Pinky's Pizza, the voice on the other end belongs to George Lucas.
When Charles Martin Smith pulls up on the Vespa in the beginning, his crash into the building wasn't scripted. He genuinely lost control of the bike, and Lucas kept the cameras rolling. Fortunately, the accident and the actor's reaction to it was in keeping with his character. Furthermore, the incident got the first big laugh from the audience in its first public premiere which Lucas and friends took as a very good sign for the film.
Wolfman Jack, who played himself in the movie, was specifically chosen by George Lucas to play a role in the movie because Lucas remembered listening to him on the radio when Lucas was in high school.
Harrison Ford was asked to cut his hair for the film. He refused, stating that his role was too small and offered to wear a hat instead.
George Lucas: can be heard as the voice of the pizza man who Wolfman Jack prank calls at Pinkie's Pizza, just before Curt sees the Blonde in the T-Bird for the first time.
George Lucas: [THX 1138] License plate on John Milner's car is "THX-138". THX 1138 (1971) is a film also directed by George Lucas. This number plate is on display inside 'The Main House' of LucasFilm's Head Office at Skywalker Ranch in Marin County.