If you had access to a time machine, what concerts would you go back to see?

Elvis, most any time, anywhere. If I had a time machine, let's go with the Million Dollar Quartet session at Sun. 

Beatles,  rooftop impromptu concert during Let it Be sessions.

Fleetwood Mac, anytime between '75  Fleetwood Mac album release and Tusk tour. 

Bob Seger, anytime after release of Night Moves album, preferably 1976-early 1980s

eagles hotel california tour, pink floyd (but after the breakup so it was only david gilmore, still great, sting w concrete blond -great opening band, elton john , aerosmith , jimmy buffet, james taylor(last 2 outdoors, something special about that, and  someone i imagine few of you have ever heard of-steve forbert in a little (400-500) seat venue. worst- tom petty(and i love his music)but so loud had to stand outside the auditorium doors to listen.

The Police at My Father's Place in Roslyn, NY, October 1979

Another thought

  Going back to buy a sports almanac. 

1969 King Crimson Hyde Park.