Other mistake: In the scene where the family is almost at the hotel, Richard asks Frank what time it is. Frank looks down (as if he is looking at his watch) and says "Two fifty-nine." Frank is not wearing a watch in any scene in the entire movie, especially given the fact that both of his wrists are bandaged from his suicide attempt.
Other mistake: At the end of the movie the VW bus still has the broken clutch and horn as evidenced by the family needing to still push the bus to get it going (and the horn continuing to sound). But they had time to fix the sliding door so why didn't they just fix the broken clutch/horn as well? Unlike when they were driving to LA, they weren't on any time crunch going home. They could have either fixed the van or just got a rental to drive home.
Other mistake: The VW has no clutch, so it would not be able to reverse, however at the gas station and at the hotel, it is parked backed up in to a space they couldn't have driven right in to. At the gas station at least they could have easily parked alongside the highway.
