Everything that can't be removed. Even without the optional ones, there's always the collar. If you were able to complete it, either there is some way to remove the collar that I'm unaware of, or somehow you were able to complete the Alex questline without removing your collar even though the button is not even clickable for me. It seems very weird that there would be a way to remove the collar without the game immediately ending, because as far as I can tell, the main quest is "find a way to remove your collar." If that is possible and there's more gameplay after that, then I guess there must be another main quest that you only acquire after completing that one?