Jack and Ally are walking toward each other in a gas station parking lot during the trip to Arizona. Ally is wearing a blouse when the shot starts, but when they meet and embrace, she's wearing a leather jacket.
Ally sings just one chorus and five spoken lines of her song in the parking lot yet somehow Jack is able to do a full arrangement of the song the next day and knows the full lyrics to it and they sing together perfectly.
The goof item below may give away important plot points.
Just before Jack hangs himself, he feeds the dog inside the house. then goes into the garage, shutting the dog inside the closed house. Later, when the audience is shown Jack's
legs hanging, through the garage windows, the dog is outside in the driveway.