Friendship
The most valuable thing I find in a friend is the ability to accept you. To accept you for who you are. To accept you, no matter where you are in life right now.
Friends should accept you and the changes you make in your life. If your friend doesn't support you changing your hair color, or leaving a toxic group(wither that be friend, work, club, or religious.), then ditch them.
Friends should accept you on your various stages of life. They should happy for you when you achieve something, and they should stick by you when things get hard. (They are not your friend if they are only around when you are happy and/or achieve something.)
Maybe I am asking for too much in this trait, or maybe I am asking for the bare minimum. At this point in my life I don't know.
I just know most of my friends have this trait, and if they didn't, we would have fallen apart years ago.
There are exceptions to this rule of sticking around. If I am hurting my friend somehow, please leave. Don't accept me as an abusive person, tell me off, and leave if you need to. (This is also a trait I find valuable: To leave someone, even if it is me, for your own good. Hopefully I will understand in time why you did it.)