Pushing the Envelope

What could possibly be in here?

UPDATE: OCT. 22, 2017

Answer: photos from the sound check before the Who’s January, 1967 show at the Saville Theatre. The opening act that night? Jimi Hendrix.

Here’s one of the photos from that envelope, one that was in the running for Alec’s book¬†London Rock but ultimately didn’t make the cut.