One of the biggest things that has frustrated me with using Google Docs in Math is the Equation Editor is too lite and has drawbacks (see my post on my other possible Add-on) and the difficulty of graphs to the document. There are a lot of amazing graphing resources out there, my current 2 favorites are +Desmos and plot.ly. However, to add these elements to a Google Doc, you need to open the new window or tab and then take a screenshot and add as an image to the Doc.
To combat all of these steps, I created the gGraph script which I am in the process of trying to publish as an Add-on.
Clicking on the Preview Graph button generates the graph as an image on the standard Cartesian Coordinant Plane (from -10 to 10). You can then drag and drop this image anywhere in your document!
I am super excited about this and it has taken me a long time to figure out what is allowable from the HTMLService standpoint. Feel free to suggest any options you would like to see!