The Whip is an amazing phenomenon, whereby once you're in it, everything is free for the rest of the event / evening / weekend. It works like this...
At the start of the event you hand over the contents of your wallet to appointed The Whipman. Thereafter anything that needs paying for is done so by The Whipman, leaving you to enjoy the event without all that faffing about in your back pocket.
There is only one rule of The Whip: Never leave your Whipman.
The Whipman is usually selected, by peer pressure, before the event starts and the post is often held by somebody who has never attended that particular event before. The theory being that, because of their ignorance, they won't stray too far from the pack.