Grabbed from https://github.com/matschaffer/profile, and slowly but surely ripped to pieces from there.
On a brand new mac, to set things up the way Mike wants things, try this:
curl -O https://raw.githubusercontent.com/sixty4k/profile/master/bin/setup_new_mac.sh
./setup_new_mac.sh
From here you can now put any *.conf in ~/.profile.d and it'll get loaded in alphabetical order. You can also make directories that end in .conf which profile will then load all the .conf files in that directory in order.
This profile loads init first, followed by all the .conf files in .profile.d/core, then any .conf files in .profile.d. This way you can put any general use configs in core and anything personal in .profile.d. If you want to keep your personal profile information in git, just set up core as a submodule to your personal repository.