Kris: writes about himself, and weird doodles on the sides
Tao: rants / burn book (Just like Regina George)
Chen: his diary/plans on pranking and trolling
Xiumin: plans in his future life and adventures
Lay: names of people and their infos / reminders
Luhan: writing about his daydreams and nightmares
Suho: to buy things and lists of those who owe him money
Chanyeol: writes about to what happened to this day, detailed with reactions on the sides and writes about how amazing some people were
Baekhyun: writes about his crush, fanfics of him & crush, his beautiful life
Kyungsoo: *coughs* Deathnote
Kai: his goals and techniques on How To's
Sehun: writes about his complaints about his hyungs and his hate to the world