Life's Little Things - Finding Cash in Obscure Places!

I generally don't have any cash on me. Whenever I do it's because I'm going to go out some place special. Whenever I open my wallet I jokingly say, "What's that green stuff?". I've had cash on hand for events last week, and still had some leftover. 

For the race today, I packed a little wallet with my ID, cards and some cash. After breakfast I peeled off drove out of the parking lot I lost track of it, which I think I initiallyput on my passenger seat. When I got back to my apartment it. was. gone. Gah!!! I got my flashlight and started frisking my car like crazy. 

I eventually found the wallet hiding between the seat and the door on the passenger side. BUT I found a crisp $10 the depths of darkness between the driver seat and cup holders. Whah?!?!?! Where did this come from. How long had it been there? Who cares?... SCORE!!! 

What should I do with this?!?!?! 

When was the last time you found cash unexpectedly?

What did you do with it?