-Father dies before he can remember
-Mother abuses him
-Aunt who is kind of responsible for the death of his mother, takes him in and abuses him.
-Goes on a date with a hot chick with similar interests. Hot chick turns out to be a ghoul, tries to eat him.
-Hot chick gets killed right infront of him, he gets injured as a result.
-Becomes the science experiment of some crazy doctor that's trying to create freakish ghoul-human combinations.
-Can't eat normal food anymore.
-Primal urge to kill and eat people grows out of control.
-New changes to his body make him even more of a social recluse, as he has to hide the changes, he cuts off contact with his best / only friend.
-Group of ghouls help him out, show him the ropes, become his new family.
-Child staying at the coffee-shop grows affectionate towards him, he watches as the child's mother is hunted down and slaughtered, as he stands by and can't do anything about it.
-He meets a new friend his best-friend has made. This person then tries to kill them both, driving Kaneki to the point that he nearly ate his best friend.
-He makes a new friend, plays squash with him, goes to coffee shops and talks about books with him, only for new friend to try and sell him off to be slaughtered and eaten before a large audience.
-New-friend stops the show, saving Kaneki. Then later prepares a scenario where he kidnaps Kaneki's friend's girlfriend, with the intention of feeding her to Kaneki shortly before new-freind eats Kaneki.
-Kidnapped from his 'family' at the coffee-shop by a terrorist ghoul organization.
-Organization forces him into slavery.
-Higher-up in organization takes him for 'personal' use, subjects him to excruciating torture for days.
-Torture causes him to mentally snap, and embrace his 'ghoul'-side, becoming a cannibal.
-Breaks out, only to find his 'family' members in danger as they tried to rescue him.
-While looking for answers, he finds the base of the doctor that turned him into a ghoul, only for one of his 'family' members from the coffee-shop to come in and steal away the hot-chick from the beginning - clearly they've been lying to him about some things.
-Gets his ass handed to him while exploring secret-base. Goes slightly more insane as a result / in defense.
-Abandons his new posse in an attempt to help out his 'family' when their location is discovered, despite it being basically a suicidal decision.
-Helps a few of the members, tells them to head out through the tunnels.
-Gets stopped by a CCG agent he seems to like / doesn't want to kill, but has no other option. Gets part of his body ripped off in the fight and believes he kills the agent.
-Hiding in the sewers to regenerate, he comes across his best friend, who Kaneki believes that he then eats before passing out.
-Stumbles through the sewers to where he told his other friends to escape through, finds the ground littered with their corpses. He then creates the delusion that the ground is rather covered in flowers.
-The man responsible for slaughtering his friends in the tunnels then brutally 'kills' Kaneki.
I'd go on, but there's just too much suffering. Plus I'm sure I already missed some things.