My best find when doing a pre-race circuit walk was a transponder - which my mate beat me to.....and at Croft last year a Snap-On 10mm spanner
Best ever find at a circuit was many years ago when queuing to get in a GP at Silverstone when I found a entry pass.....I did briefly think about holding it up and asking - "Anyone lost this"? before concluding that eliminating the 400 applicants might be tricky.....