Well, in your case, one thing you could potentially share is that you tend to cover dark feelings with humor and/or use it as a defense mechanism. I do the same thing--my T has said it's common and that he does it as well. But it could be good to share so that if you seem to be joking around, it doesn't necessarily mean that you're doing OK.

Making a list to share seems like a good idea.

For me personally, something I told my T early on is that I tend to get attached to male authority figures, including therapists. I think he mistakenly thought he'd be immune to it because he's not warm and fuzzy like my male marriage counselor was. He has since very much learned that he is not! But I did warn him.

I think for me, something else important is that I can seem fairly high-functioning, like be getting my work done, etc., but it doesn't mean I'm doing fine mentally.