How did he get out? The law requiring trunk releases wasn't in force then.
Perhaps it was a station wagon or a jeep.
I don't know. In Sonny's "autobiography",Hell's Angel: The Life and Times of Sonny Barger and the Hell's Angels Motorcycle Club (Sonny Barger, Keith Zimmerman, Kent Zimmerman), Barger says that when the fighting broke out in earnest, Hunter Thompson jumped in the trunk of his car, closed it, and whimpered like a bitch.
Needless to say, Hunter is not on Sonny Barger's Christmas card list.