On instruction from John Hughes, Edie McClurg's role as the St. Louis rental car agent was partially improvised. Hughes told her to simply riff a fake phone conversation with someone about Thanksgiving plans while Steve Martin remains waiting in line staring at her to finish up. McClurg came up with the idea to speak with her sister about who was going to make what adding "You know I can't cook!" Hughes asked her how she came up with those lines so quickly and she replied that, like his scripts, she just drew it from her own life. McClurg claims to this day that random people ask her to tell them they're fucked.
Steve Martin was convinced to join the production after favoring two scenes he had read from the script: the seat adjustment-scene in the car, and the F-word tirade at the car rental desk.
Steve Martin talked in an interview about his late co-star John Candy and his similarities with the character of Del: "Well, he was a very sweet guy. *Very* sweet... and complicated, and so, he was always friendly, always outgoing and you know, funny and nice and polite, but I could tell he had kind of a little broken heart inside him."
The exterior of their aircraft in flight is a re-use of the 707 flying through the storm from the movie Aterriza como puedas (1980), also released by Paramount Pictures.