The Google Doc adds-on offer some new capabilities and a great way of expanding the power of apps in general.
I am putting together content that will eventually be divided between a textbook and related online resources. My work flow results in one giant integrated file and I eventually decide what I will end up putting where.
In the image that appears above, you see the Table of Contents as a second window to the right of the open doc. The one technique I had to add to my normal approach is to identify my headings as headings (I usually just bold my headings). If you are familiar with HTML headings, you are ready to go.