|Jack Schmitt is using the lunar rake. It was designed to collect medium-sized rocks more quickly than any other method we could think of. Jack Schmitt was like a kid in a candy store, the first geologist on the moon. What better place for a scientist in this generation.
In the painting, we can see the entire backpack. The larger, lower module is the Portable Life Support System, or PLSS, which provides oxygen to breath and to pressurize the suit, water to cool the astronaut, and two-way radio communications. The smaller, upper module is the Oxygen Purge System, which was carried for emergency situations such as failure of the PLSS or a space suit leak. Fortunately, we never had either.
A sample bag can be seen on the side of the PLSS. It makes a convenient place to store lunar rock samples.
We all studied geology in our pre-flight training, as it was NASA's idea that it was easier to make geologists out of test pilots than the other way around. Easier maybe, but I think Jack will agree, not as much fun.