Dennis's son had not finished his sandwich when they left the park. Where did the bag go?
The film shows James Dean romancing Pier Angeli in the opening two months of 1955, and being devastated when she abruptly marries singer Vic Damone. In fact, the brief romance between Dean and Angeli had been well over a year earlier and her marriage to Damone had been in October of 1954. At the time of the events of this movie, she was pregnant with her first child by Damone.
The film is set in the early part of 1955. James Dean and Pier Angeli are seen attending the premiere of the Judy Garland version of "A Star Is Born", a film which had opened in New York in September of the previous year, and in Los Angeles less than a month later.
The film shows James Dean hoping to be cast in "Rebel Without A Cause" throughout the proceedings and only being finally given the role (by Jack L. Warner himself) during Dennis Stock's rural photo-shoot in February of 1955, a short time before the commencement of filming. In fact, Dean had been confirmed in the role at the insistence of Nicholas Ray before the end of 1954, ahead of any of the other actors.
Pay phones in 1955 did not have metal cords or the receivers shown in the film.
At the time the film is set (1954-55) it was not possible in Southern California to direct dial outside of a local calling area. Only an operator could place the call. At the time, area codes were used only by operators. Not until 1968 was it possible to direct dial calls beyond the local area. In 1955, in areas controlled by General Telephone (Santa Monica,West L.A., Malibu etc.), local numbers required dialing five digits. Other calls required an operator. In Pacific Telephone (Bell) areas (most of Los Angeles County), local calls required dialing seven digits; other calls required an operator. It was not yet possible to dial direct to New York; it was necessary to first dial 112 for long distance and have the operator place the call.
Dennis Stock (Robert Pattinson) appears to look at the back of the camera after each shot, throughout the movie. In modern times with a digital camera this would make sense as it would show a preview of shot just taken , but with film cameras this does not apply. There is nothing to see.
When turning into the road to the farm, steel power poles are obvious. They would not have been in use at that time, certainly not in rural areas.