Id keep it. Without question. I would also assume that because its $50,000 in cash it is there because of something illegal, thus taking it to the cops would be foolish. I would sit on it for a bit, pay attention to the local news to see if it was a bank robbery or if it was just some drug dealers stash, or whatever. If after a month or so nothing came up about a large sum of cash being taken/robbed then I would trickle spend it. Never touching a bank but what this money would allow me to do would be to pay for all my daily expenses in cash and save my paycheck. Say I wanted to by a motorcycle. I would buy it used off of a private seller and pay cash, I would not in any way shape or form let anyone know that I stumbled upon this money, friend, foe, or government official.
Pretty much this.
As long as you are smart about it, you should be safe. Besides, the cops where I live are so crooked they would keep it for themselves anyway. That is not even remotely a joke.
I'd pick it up and be all "Maaaaaan money doesn't buy you happiness" AND THROW IT ON THE GROUND.
Yes! Pick it up, look to the sky and say: "You must think I'm a joke. I don't need you hand outs, I'm an advlt!" Then THROW IT ON THE GROUND.