I was at the Stones concert in Hyde park on the 5th July 1969! (showing off my age now!)
Sat on my arse for over 8 hours and there was no way you could leave otherwise you could not get back to where you were sitting.
I am just behind the black geyzer gyrating around in the crowd if you look at the very grainy video of "Stones in the park"
Ended up sleeping in the Roundhouse theatre under the bar and did a runner in the morning. Also jumped the barrier at the nearest tube station to get back to south Londun where I was living at the time.
Great day though!!