So just type it like you are talking to yourself.
Think about the scenario and what should be inside the box with general outline. Then after which think outside the box, and add things that could appear in the future.
Since it's just a draft, don't write what you don't want to, that can be done later to fresh out the story. For example, exclude dialogue and details.
Let creativity flow, it doesn't have to make sense nor does it have to be in order. As you can piece it or select it later.