I found £5000 in £10 notes when an old dear left it under her seat!
She was having an attack of diabetes and had checked her insulin in to the hold. She was so obsessed with getting off the jet to take her medication, that she forgot her life-savings that she was carrying with her!
I went into the arrivals hall where I did a P.A. announcement that "someone left something very important" on board that flight....she hobbled around on her zimmer and her legs about gave away under her when she realised!