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The green convertible is a 1986 Chrysler LeBaron Town and Country, with a 2.2 liter turbo engine. It was modified for the film, including the following Dodge 600 parts: tail lights, steering wheel, and owner's manual which can be seen in the glove compartment when Neil puts his wallet in there. The trunk was from an older K-car convertible: no third brake light, and the luggage rack that was not offered in 1986, but was on older models.
John Hughes, in an interview on the "Those Aren't Pillows" DVD, said he was inspired to write the film's story after an actual flight he was on from New York to Chicago. The flight was diverted to Wichita, Kansas, taking him five days to get home.
The exterior of their aircraft in flight is a re-use of the 707 flying through the storm from the movie Airplane! (1980), also released by Paramount Pictures.
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.