I've said it before: If I ever found an abandoned gun (or knife) in the "sterile" area (airside or on the plane), I would discretely wrap it up in a barf bag or paper and throw it out in a trash can, never to be seen again. In the bathroom, it's a pretty short trip from the toilet stall to the trash can, and it's unlikely a TSA clerk will be in there and decide to search you.

What would I _not_ do? Turn the weapon in and have to deal with a terminal dump, terminal lockdown, and/or having to take Greyhound home.

Another alternative is to simply ignore the weapon. Of course, this opens the possibility of someone else finding it, reporting it, and resulting in a dump/lockdown.

Of course, there is a risk to this: if TSA clerks decide to start deplaning passengers on your flight and you found the weapon on the plane...