In the review of Mrs. Brown's Kooky Kookie, Oliver mentions that he'd been told that David Copperfield kept a Dinamo standing by offstage to cover unexpected stage waits.
Not sure that anybody's interested, but in at least one show it was not only there, Copperfield used it.
I was at one of the tapings for his 1993 Fires of Passion TV special. At one point there was a glitch and things had to be reset. While the crew was resetting, Copperfield walked to the side curtain, reached offstage and brought out a Dinamo and performed it (although I thought it was Tenyo's What's Next- but I was in the last row of the theater so didn't have the best view).
Later in the show there was another unplanned delay. I don't remember his exact words, but after a short pause Copperfield said something like "well, I'm not sure what to do now... I already did the dot trick". For some that seemed much funnier to me than the rest of the audience.