Often when it I’m in the middle of a story, and I’m getting low on paper, and I don’t want to venture out into the “wiggly-world”, I’ll grab a page of unfinished art that I have lying around and use the other side.
Here’s an example. This is page 120 from Dark Matter, before the final lettering was in place.

And on the other side of the above artwork is an unused page of art from the first chapter. These blue pencils are an earlier version of page 20.

And here’s the final version of page 20:

Next time more lost art retrieved from the jaws of those feisty grey aliens!