My cousin's ex-girlfriend is a flight attendant, and she has quite a few items in her possession that people have left on the planes. However, she always attempts to locate the owner before she takes the items for herself, so she's one of the honest "finders."
I believe there is a lost and found policy at the airport where if items aren't claimed by a certain time, then the "finder" has the option to keep them. A couple of the things she acquired: a really nice camera someone left in the plane and some fly fishing rods. Don't know how someone forgets about their fishing rods, but apparently it happens!
Sorry to hear about your sunglasses, though! I used to work in a restaurant, so I know how things have a way of "walking off" from a table.