The Apollo 11 astronauts left a variety of items on the moon.  In addition to the flag, the plaque, and the silicon disk with goodwill statements, they left the item shown above.  It is a small replica of an olive branch, described as "less than half a foot in length," a traditional symbol of peace.   The gesture was intended to serve as "a wish for peace for all mankind."

Photo:  Great Images in NASA, via Fresh Photons.