If I'm angry at the therapist, I usually think about how I'm going to confront her. Sometimes there is an element of fantasy about it. Other times my planning involves checking my rage enough to formulate how I'm going to confront the therapist without being inappropriate in my behavior.
Since I can be manipulative, I have sometimes planned to manipulate the therapist about something. I can be kind of controlling when I feel threatened and vulnerable, and that happens frequently in therapy. Unfortunately, attempts to manipulate the therapist sometimes backfire on me. Not always.
Mostly, stuff just pops in my head when I sit down to have my session.