I was on Expo aswell, fortunately I padlocked my tent (OK, no great security measure, someone could obviously cut through, but thats a bit obvious...), and packed it onto the coach before leaving for the track on Sunday.
HOWEVER.... my brother is convinced he was pick-pocketed. This being due to the fact he had a wallet type thing attached to his belt with his money in. Although to open it you would have to unclip it, unfold it, unzip it and remove the cash, and then zip it up, fold it, and clip it again, all without being noticed (he didn't realise he'd lost all his cash till he opened it 

 ). I'm sure it would take a pretty determined pickpocket to do this, which makes me think he may have dropped it somewhere, though he insists he counted his money on the way to the track on the coach, and put it away safely...
Fortunately I had enough money to see him through for food and stuff, but sadly he last over £100, however the tour company we went with may be able to get it back on the insurance.
I made sure of keeping my money in several places, which worked fine...