Rounding out the tale of how The Lord of the Rings was written, with the final chapters in Mordor, the rejoicings after, the Scouring of the Shire, the end it now has, and his intended epilogue, where much that got relegated to the appendices about future history was put into a conversation between Sam and his children over the age of five. (Several below had already been packed off to bed.) Much less flexibility than in the first volume, as the plot builds up steam.
Then it's filled out with some stuff he worked on about this time. The Notion Club Papers contain very little about even Middle Earth, and I skimmed most very lightly, and then a bit about the fall of Numenor.