Mental Floss magazine had an interesting article in a recent issue discussing items left behind on the moon by the astronauts, including (1) a gold-plated olive branch, (2) Alan Shepard's golf balls, (3) a shrink-wrapped Polaroid of Charlie Duke's family, and (4) various other items such as moon boots and "defecation collection" devices.
After reading through the list of items, I starting thinking of what future generations or even distant visitors would find on the surface of the moon. We know the Apollo missions left behind the lower portion of the lunar modules (see NASA map to the right). In fact, NASA's Lunar Reconnaissance Orbiter spotted five of the six landing sites in July 2009. the LRO also spotted scientific equipment the astronauts left behind, as well as the footpath created by the astronauts using these instruments.
We also know that various crash sites can be found on the moon (and I am not talking about Transformers 3). For instance, as recently as October 2009 NASA crashed the Lunar Crater Observation and Sensing Satellite (LCROSS) into the moon's south pole in the hopes of stirring up some water (this satellite is associated with the LRO mentioned above).
A review of Wikipedia's list of moon junk shows mankind has left behind about 187 tons of material. And while the United States and the former USSR are in the lead as litterers (both left 30 spacecraft on the surface before the first man even landed), objects have also been left behind by Japan, the European Union, China, and India.
We shall see if the Chinese beat the other nations back to the moon, but the first race was quite spectacular. For instance, while the United States will always get the credit for the first man on the moon, the Soviets were not far behind scientifically with their Luna 16 spacecraft (shown to the right) bringing back moon samples in 1970 (following the successful return of samples on the Apollo 11 and 12 missions). However, the Soviets stopped sending craft to the moon in 1976, while the United States and other nations continue to explore the moon's surface.
Someday we will have moon archaeologists who will recover these odd objects and probably find some new stories among the wreckage. And earthlings are doing their best to leave junk in other parts of the solar system, as the Voyager spacecraft shoot out of our solar system and into the great unknown. The story (and litter) has just begun.