I think that the little abandoned car has so many meanings. First, it shows how little Michael was involved with his family, abandoning them on Christmas and allowing others to pick out their gifts, not even knowing what those gifts were. Anthony treats the gift as it should be, a toy given without thought or love. If he felt that the car came from his father's heart, perhaps he would've taken greater joy in it. I think that abandoned car and the subsequent conversation with his mother (one of the best scenes in the movie, imho, and one of the few times we are allowed to get any insight into Mama), Michael also sees the difference between how he has chosen to run his families (upper and lower case F's) vs. how his father did. Can you imagine Vito leaving his family on Christmas? Leaving it to a stranger to pick out their gifts? Never happen.