Tina Chen, who played Arlo's on-screen girlfriend, wore an authentic Chinese dress that had belonged to her grandmother. When they wrapped up the shoot, the film crew put the dress in storage. She never got it back. In case you didn't know, Arlo Guthrie's real-life wife, the former Jackie Hyde, is not Asian. Shelly Plimpton, who played the 15 year old groupie in the movie, was actually 20 years old at the time.
Stage lights are clearly visible.
Also, keep an eye on the leaves. The movie was filmed over a 10 week period beginning in October. The scenes in the church were some of the earliest. If the Thanksgiving scene had really been shot around Thanksgiving, there would be few leaves left on the trees. Instead they are at their peak colors.