Never found anything 'good' other than the odd banknote in the street (Charlotte spotted £20 on a traintrack when she was young and I retrieved it with a stick and some gum.

BUT

1994ish when I was working for KPMG. Had to give an evening presentation in Frankfurt on a friday. Did not realise it was Oktoberfest.
Straight after we all went to the town square and consumed a number of large steins. Could not even remember which hotel I had checked into earlier so the Managing Partner in Frankfurt called a cab and I passed out on his sofa.
Got up in the a.m. and realised I didn't have my briefcase with laptop, passport, ticket etc. etc. and must have left it under the table we were sitting at in town square.
We drove back there. Square was still buzzing - people drink 48 hours straight at Oktoberfest - briefcase was still there, no-one had even noticed it.