Store basic config files and scripts to get your new environments the way you want them :)
This should be obvious, but in case it is not:
THIS WILL OVERWRITE A BUNCH OF DEFAULT CONFIGURATION FILES. USE WITH CAUTION.
Heavily patterned off https://github.com/CardenB/dotfiles, but with key differences for certain files that I use differently. Also, unlike Carden's repo, this does not use Ansible. This is bad in a lot of ways (doesn't allow for as easy use on many remote machines simultaneously, doesn't strongly support idempotency) but has the critical advantage of being a little simpler and less demanding in its assumptions.