Google Docs – How to Create an Online Collaborative Document with Section-Specific Editing

You can create a table of Contents in Google Docs;

1. Add headings to your document by clicking Format > Paragraph styles in the toolbar, and selecting a heading.
2. Click Table of contents from the Insert menu. The table of contents appears wherever you've clicked in the document, so make sure you place your cursor where you want to add the table of contents. If you need to move the table of contents, select it as you would select text and either move it with your cursor or cut it and paste it.
3. You can continue to add headings to your document or change current headings. However, if you'd like a change to become part of the table of contents, you need to click first the table and then the Update now button.
4. Each item in your table of contents links to the titled sections of your document that use the heading styles (that you added in step 1 above).

http://docs.google.com/support/bin/answer.py?hl=en&answer=106342

Hope this helps.

Lars Kellog-Stedman created a great little python app called gitdriver which I found on this answer at StackOverflow. It does what you're looking for. It authenticates to Google with OAuth and pulls down all the revisions of a document, committing them to a git repository.

With this, you could fetch a versioned copy of your Google Doc and then work with it using traditional git tools.