Unfortunately, you are unable to download your DigitalOcean snapshots and backups outside of the DigitalOcean environment. They have not made this feature available.
You can do a lot with DigitalOcean snapshots within their network. Create new droplets from Snapshot, restore existing droplets to snapshot and moving snapshot across data centres.
DigitalOcean has talked about making this possible but we have not seen DigitalOcean make any steps towards making this possible.
If you want to download the snapshot just to be able to recover a couple of files, the alternative is to create a new droplet from your existing snapshot. Then you can either boot it normally and SSH in or more recommended start it in recovery mode by hand and extract the files that way.
DigitalOcean offers the ability to transfer a snapshot from one region to another. You can perform this action via the web console or API. SnapShooter offers region replication you can lean more here Cross Region Replication