Rolling Stone Cameo
In a scene near the end, when the main character is in New York, he attempts to enter a taxi, only to find that it is already occupied. The man in the cab is the real publisher and founder of Rolling Stone magazine, Jann Wenner.
Peter Frampton as Reg
At the part in the movie when Stillwater's ex-manager, Russell and other band members are making deals with cards, the person who is playing against Stillwater's ex-manager is "Reg from Humble Pie". There was no member of Humble Pie by the name of "Reg". The person who plays Reg is Peter Frampton, the guitarist/vocalist for Humble Pie.
Cameron's Hand
During the opening credits, the hand that's writing on the notepad belongs to Cameron Crowe, the writer/director of the movie.