The tool that makes this possible is gsutil, specifically its rsync option. This works very much like the usual rsync command in Unix but lets you perform bulk transfers/synchronisation of files between a Google Storage bucket and your local machine.
So for my specific case where I wanted to have everything from Cloud Storage copied to my laptop, I would use a command like this...
This would make a mirror copy of my app's default bucket files on my laptop in the local /Backups/backup-files directory. The -m option makes transfers run in parallel, speeding up the entire backup. The -d option will delete any local files that are not in the Cloud Store bucket. The -r option performs a recursive copy of all the bucket data.
The output looks something like this (truncated)...
This operation can also work in reverse, that is making the Cloud Store bucket a mirror image of the local file system; effectively restoring data that was backed up earlier. Doing that requires the source and destination arguments to be swapped, and possibly not using the -d option when copying back to the bucket.
Of course this will only back up the files and doesn't touch the Cloud Datastore, this is a topic for another post.