Go till you can't go any more, sit down in an uncushioned hardback chair, hold a serving spoon in your hand, put a metal plate under where your hand hangs, sleep until you drop the spoon and the spoon hitting the metal pan wakes you up.
It's said that he could go another 4 to 6 hours after that type of nap.
I also heard he used to lie on a pool table with a pool ball in each hand, stretch out over the edge.