Not my all time favorite, but I was visiting a neighbor in a lighting booth @ a Rod Stewart/Faces concert (1970/1971 Veteran's auditorium, Des Moines) and Rod would run back behind a large speaker cabinet stack and have a makeup person mess up his hair and apply water (sweat) to the collar of his shirt.
This, of course, was not visible to the audience (even from the balconies).
The lighting control booth was located above the back/right stage.
Another one was a Van Morrison concert in which Van came out in a little dude cowboy suit/outfit (Pee Wee Herman eventually adopted a similar style in clothing).
However, both were great performances/concerts - though Van kept stepping away from his mike and yelling @ the stage crew through most of the concert (he was perpetually pissed about something).
Last, but not least, were numerous concerts in which Ted Nugent and the Amboy Dukes were the opening act.
Ted would make his appearance (wearing tights and a cape) by jumping from an unseen platform down to the middle of the stage.
Back then you could leave and re-enter concerts and we would leave until Nugent was through with his set.
DeKay