I run Emacs on both Windows and Mac machines. On Windows, my ~/.emacs file (called .emacs_windows in this repository) loads ~/dropbox/.emacs and then ~/dropbox/.emacs_custom-windows. The setup for the Mac is analogous.
Some of the .emacs code uses conditional tests to see whether it is running on a Windows machine or a Mac machine and take different action in each case.
The code is lightly documented with links to sources for the things I am using.
I have recently started using John Wiegley's use-package for loading packages. Not everything is converted and I may convert other packages to load this way.
Orgstruct mode is turned on by the first line of the file, so pressing tab or shift-tab will collapse or expand the file into or from headings, as in Org mode.
Some more background information is given in the blog post My Dot Emacs.