I would not give the waller to the police they would keep the money. I woukd try to trace the owner. As a child I once found a fat wallet between the bread I took it to the cashier. There she stood the woman who had out it down and forgot it. She responded as if I had robbed her. Just like with @ibesso she did not give me the 10% finder's loan" as it calls here. If the cashier wouldn't have been present she might have hit me.

I once lost a wallet and no honest person around. Instead if cash your debit card is read - the great thing of contactless payment versus technology.