Since there's no games to watch (other than DVDs of games from the 80s and 90s), I'm breaking out my Bills library.
Personal favorite: "OJ Education of a Rich Rookie". Behind the scenes look at the 1969 season that's pretty revealing and entertaining. Lots of stories about the last days of the 1960s Bills crew, including Maguire, Day, Kemp, Shaw and many more. Great photos and lots of game day details. Enjoyed this as a kid and it still holds up for me.
I have a dozen or so Bills books written by or about former players and coaches. Many good ones in there and some real stinkers.
Interested to hear about others' favorites.....