Along with an American flag, astronauts initially left a patch honoring the fallen Apollo 1 crew on the moon, as well as a plaque that reads: "Here men from the planet Earth first set foot upon the moon. July 1969 A.D. We came in peace for all mankind."
Since then, as The Atlantic has reported, approximately 400,000 pounds of material have been left on the moon. This includes unmanned space vehicles, ascent and descent stations, moon buggies, golf balls, and a family portrait belonging to Charles Duke of the Apollo 16 mission.