In the book, Hunter S. Thompson listens to "Sympathy For The Devil" by The Rolling Stones. The rights to play it in the film were too expensive for the production's budget.
Terry Gilliam took over as director after Alex Cox left the picture due to creative differences. Gilliam re-wrote the entire screenplay in a few days to fit his unique creative vision and style, while staying true to Hunter S. Thompson's writings.
According to Johnny Depp, the gorilla statue outside the Bazooko Circus now "lives" in his front yard.
Hunter S. Thompson shaved Johnny Depp's head. They were in Thompson's kitchen, Depp refused to look in a mirror, and Thompson wore a miner's hard hat.
According to Terry Gilliam's commentary on the Criterion Collection DVD, at the beginning of the movie when they stop on the side of the road after Duke starts seeing bats and wants Gonzo to drive, a strange looking cactus is in the background. It was designed by Ralph Steadman and appears many times in the background of various scenes. Gilliam complained of having to lug it around wherever they went.
Terry Gilliam: Wearing a cap and holding a microphone protruding from a large tape recorder box in the motorcycle race, as the bikers take off.