When Nat and Ritchie start out on their trip, Nat makes Ritchie pull over quickly to get a haircut; a tollbooth is visible in the background. Later in the film In the background you can see a toll booth. Later in the film the same tollbooth is in the background when they swerve off the freeway.
Nat tells Richie he's taking a picture of him beside a '63 Corvair. The '63 Corvair has a straight vertical front end; the Corvair hulk they are standing by has a curved front like the '67 Corvair.
As Nat is leaving for New Mexico, he says he's "Only taking the good stuff--Louis Vuitton." But all the bags he's carrying are Gucci.
In Altoona, Pennsylvania, Nat and Ritchie talk about how this is where Ritchie was convicted and went on to do time in Rahway. Rahway is a prison in Jersey; presumably a person convicted of a crime in Pennsylvania would go to prison in that state, not in New Jersey.
After getting off the highway in Amarillo there is a sign for the Atlantic City Expressway.
They stop at an IHOP in Altoona, Pennsylvania--where there isn't, nor has there even been, an IHOP.