Piece of paper.
Pen or pencil of your choice.
Or a computer screen.

And just start writing. Write about how you feel stupid writing. Write about how angry you are, about how sad you are, about how your T's chairs are comfortable or not, about how your eyes are tired or your left ear itches or your how your head feels when you want to yell and can't. Imagine you're speaking to your T, or imagine you're alone at the south pole and talking to a penguin.

I'm not being silly. Just go ahead and write, let the feelings and thoughts flow out of your head. No one is going to read it but you, so it doesn't matter if it makes sense or is "right" or "wrong" or fair or even true. Just write. Eventually, the feelings will start to jell together, and you might find a nugget of truth or two. Or you might not. The process is the point, not the result. And have fun with it--draw pictures if you like to do that, or comic strips with stick figures, or whatever. It's yours.

ETA: and don't try to re-read or edit or judge what you've written. It will shut you down. Just write!