Which mistake was the dumbest of all?
So right after finding the money, they decide to count it ... right in the back of their *beep* truck sitting on the side of the road! I know it's a tiny town and they are out in the boonies, but certainly someone could (and did) happen by.
Or, was it going back to the plane and putting some of the money back? This was pretty idiotic. Not only do you give away $500K, but you have to go back to the scene and risk being seen again (which of course happened in the film). This sets in motion a series of events that leads to several murders.