Read any book you want to and meet up to talk about them, simple! Read as much or as little as you want it's really a conversation group so if you've not finished that 500 page biography it's all good.
Honorable mentions from the previous meetup:
---Books---
The Sword of Allah, Akram
Private Lives and Public Affairs, Maza
All Systems Red, Wells
Annihilation, Vandermeer
Guns Germs and Steel, Diamond
Run Away with Me, Selnick
Voyager, Yeager and Routon
The Cult of the Dead Cow, Menn
The Invisible Library, Cogman
Under the Whispering Door, Klune
Quiet, Cain
---Film, Musicals, Websites, TV and Stuff to Do---
The Davis Bicycle Collective