The Apollo missions were dedicated mostly to geology, so the more the astronauts left behind, the more rocks they could bring back to Earth. Every Apollo crew left behind seismometers, lots of geological tools, most of their cameras and their lunar module ascent stages. The Apollo 16 crew even left a gold-plated ultraviolet telescope. Apollos 11, 14 and 15 left the Laser Ranging RetroReflectors (LRRR) — and they still work. They’re vital for measuring the distance between the moon and Earth. And of course, Apollos 15, 16 and 17 all left lunar rovers.
In addition to the items from the various Apollo missions, there is another one on our celestial neighbor that has NASA interested. Impact from a rocket body left a series of craters on the moon in March 2022. None of the world’s space agencies claimed credit (or responsibility) for creating these new pockmarks on the lunar surface, so NASA is a bit stumped about their origins.