In the opening scenes when the missile officers are getting their sidearms from Keegan, it shows Keegan wearing a missile badge (known as a "pocket rocket") on his uniform and in a later scene he is wearing a security police badge on the same pocket.
Same cars in different places during the 'killer cockroach' scene set in Salt Lake City (i.e. Fiat 124 Sport seen at the garage, multi-storey car-park & parked outside a department store on the street when Tanner & Janice go 'shopping' on his bike).
As the blue sky was often used to 'key' the optical effects for much of the film, when the camera panned or moved upwards, it resulted in the special effects moving with the camera and/or revealing clear blue sky elsewhere in the shot.
After the encounter with the four radiation sickness survivors, the Landmaster drives alongside a body of water. What should be a reflection of the sky on the water isn't - it's a continuation of the blue-screen sky effects.
Despite undergoing enough environmental damage to turn most of the country into a desert, complete with mesas near Michigan, several shots feature fully intact telephone poles with wires still strung between them.