Under the heading of “mental notes”:
The Arduino IDE has a setting for your sketch directory. I have recently created a directory on my Google Drive and pointed the IDE to that directory. Also in the Arduino directory I have created /libraries (lower case, plural) and put there the class files and libraries I download.
Now on any MAC (or PC) I can edit, compile and test code and no longer need to haul around a USB drive with projects. More importantly I no longer have version splatter across the different machines – I am always working with the current versions.
To get the google drive as a native element of your MAC (or PC) you will need to download and install the Google Drive application.