[akadruid]

The same way you secure your wallet.

I can't imagine why anyone would leave their laptop / phone / other device lying around. I go out and about in London, and I don't see anyone doing this.

I suppose LAN parties are an exception, but properly organised large events have a policy of tagging all equipment coming in and checking it on the way out. I have not been to a small private event where people were allowed in without being known and vouched for by another attendee.