Jenna Fischer, who was married to Gunn at the time, was not originally part of the cast. The actor in her role begged to be released from his contract because he had an offer to shoot a pilot, so Gunn let him go rather than have a performer on set who didn't want to be there. Gunn swapped the character's gender and gave her a few more lines. By the time the movie was released Fischer had become immensely popular from The Office, so she was the one who went on The Tonight Show the night before the film opened.
In the opening scene as they pan down the street, you can see "R.J. McCready's Funeral Home". R.J. McCready is the name of the mayor, and was the name of Kurt Russell's character in The Thing (1982). Russell ended up working with James Gunn 11 years later on Guardians of the Galaxy Vol. 2 (2017).
Rooker dislocated his shoulder while filming the scene where he attacks Starla and grows a floppy arm. It was a long shooting day with multiple setups, and he didn't tell anyone until the shot was in the can.
James Gunn's intention with the character of Starla was essentially "the Hitchcock blonde," and he found it in Elizabeth Banks. He saw other actresses, but said "they had the sort of WB good looks, but Elizabeth really had that old time grace."