The green convertible is a 1986 Chrysler LeBaron Town and Country, with a 2.2 Turbo engine. It was modified for the film, including the following Dodge 600 parts: tail lights, steering wheel, and owner's manual (that can be seen in the glove compartment when Neil puts his wallet in there). The trunk was off of 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 wrote the first-draft of the screenplay in 3 days. His average writing time for a screenplay in those days was about 3-5 days with 20-some rewrites.
When driving down the highway, the road has raised reflector dots. Reflector dots are not used in the Midwest because the snow plows would rip them right out of the road.
Neal's plane ticket claims that he'll leave from JFK Airport, but with the information board in New York and the arrival board in Chicago, Neal is actually departing from LaGuardia Airport.
Del: You wanna hurt me? Go right ahead if it makes you feel any better. I'm an easy target. Yeah, you're right, I talk too much. I also listen too much. I could be a cold-hearted cynic like you... but I don't like to hurt people's feelings. Well, you think what you want about me; I'm not changing. I like... I like me. My wife likes me. My customers like me. 'Cause I'm the real article. What you see is what you get.
Del: [sitting outside the motel cafe after finding out they've been robbed]
You know I've been thinking. What we're dealing with here is a small-time crook. He didn't take the credit cards, right? So we charge our way home. What kind of plastic do you carry?