I once, aged about 20, left a backpack with all my festival medicine in at Reading train station. Not the kind you would report missing. Apart from being out of pocket I spent the entire festival shitting myself that I had I.D in the bag, I couldn't recall.
Left 500 notes in a wallet on the floor of Gatwick airport when I bent down to sort out passports, tickets etc, upon rushing back realised I was never seeing it again. I was only 17at the time and it was a LOT of money to me then. I was so pissed off.