Everything as much as possible except what you get for it can still be checked like he Kalm Traveller no longer being here. No W-Item glitch or glitch in general to get things more often than it is supposed to be (e.g. Great Gospel or Mystile).
Chocobockle dealing 9999 damage.
The Mythril Sleeper pointing out the maximum amount of everything he mentions.
Unfortunately being so good that Vincent's Death Penalty glitches because of the maximum reached, something that is acceptable after getting that far.
A Great Materia of all kinds.
Every Materia at least once MASTERed in your inventory.
Every Enemy Skill Materia MASTERed.
All LIMIT Breaks learned
All Stats maximized, HP does not count as it is all about random resetting and levelling up.

These kind of things.