Most likely one of the more enjoyable training operations they get to participate in. From Wikipedia:
Operation Christmas Drop is a tradition that serves as a training mission for the United States Air Force which started in 1952. It has since become the longest running U.S. Department of Defense mission in full operation, and the longest running humanitarian airlift in the world. Supported by the local communities of Guam, it is primarily conducted from Andersen Air Force Base and Yokota Air Base.