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)...
The operation was quite fast too. I had almost 6000 files to copy, which completed in a few minutes. Mind you it was around 300Mb of data, but transfers of many small files do not tend to make full use of the available bandwidth.
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.