When Kevin is driving from the movie set in Vancouver, British Columbia to the airport in Seattle he pulls over in Canada to help a motorist who was in an accident and unknowingly loses his wallet at the scene. When he gets to the airport in Seattle he realizes he has lost his wallet and TSA won't let him board the plan without his ID. He would not have been able to drive across the border from Canada into the US without an ID.
When Kevin drives off from the movie set, the car he is driving does not have a front license plate. In Vancouver, British Columbia where the movie is being filmed, a vehicle is required to have a front license plate to be on public roads.
In an earlier flashback sequence, when Jack (as a youth) was walking to the car after losing a baseball game, his father referred to the home run given up as a "walk off." That phrase, per the MLB website, was not used in baseball in 1988, decades after the scene took place.