I am a collector and thus I like to have my data stored on physical media.
I am looking into M-Disk archiving and will probably use a combination of external HDD for bulk storage and M-Disks for my most important games (which will also be kept in a safe).

But I would also like to hear from other archivists. Which methods and media do you use and how do you keep your registry etc.?

The structure (folder names, etc) is the one defined by the GOG downloader.

The location is an external HD for all the games, and the internal HD for the games that haven't been played or installed yet (so these end up being duplicates, but more directly accessible).

Been covered many times.
Database for storing metadata, don't use excel it will break and become unwieldy.
Fixed directory structure so that automation can happen.
Keep some meta data in the structure like date of release and platform in case you need to programmatically alter.
Backup to multiple media both locally and externally, for instance I have 2 raids and external hdd, some onsite.
Physical media takes up loads of space and is hard to keep backed up, hdd's are smaller and easier to maintain.
Collecting physical media is dead, steam killed it.

Not really. There's still a second hand market, and there are still enthusiasts who prefer physical releases.

Yes, there are still some collectors, however charity shops, boot fairs, eBay etc. Have become very expensive and new games now are just a plastic box with the steam client, unless you get the collectors edition which is a big plastic case with the steam client.

You forgot the coupon for Netflix that's usually included in those cases.

I save everything to an external hard drive located off site. Be it TV series, book, game, recipe, plan for the New World Order to take over, cartoon, movie, etc....

Oh, do you guys get a drm telly voucher also, bonus.

gogrepo.py as the tool to download the installers and extras, and also check for any updated ones.

I keep the files on external hard drive(s), with the default directory structure. For now I keep only one local copy of GOG game installers, the installers on GOG servers are the secondary backups for now. :)

I store my games on physical media too. Hard drives.

Server at home freenas with ZFS raidz3. Rotation of 3 6 bay qnap\synology NAS offsite.

CD keys stored in a text file
PC Game compatibility list
Folder structure maintained
All games playable offline.

Still have 3 300 slot CD cases but haven't opened them in years since they were all imaged years ago.

Nothing stored online unless you count the online store the games were downloaded from, anything else would be too expensive.

Used to be a nice, thick paper they printed it on. Made a real nice paper airplane. But no longer. Thin, cheap paper. First time it "lands", the nose just crunches. Get 2 maybe 3 flights out of it. Used to be 2 or 3 dozen flights.

*sigh* No one cares about quality anymore. One thing we teach our soccer moms, if they scan important records, is to email them a copy of it to themselves and bury the email in some mislabeled folder in their email account. I backup my browser bookmarks the same way.

All games less than 5Gb zipped, i store on portable external 4Tb HDD.

AAA games that i want to replay multiple times that are less than 10Gb zipped, i store on 2nd portable external 4Tb HDD.

Any game above 10Gb zipped, i consider to large to archive, so i play these games first from my backlog.

Try RAR5 compression on some of them.

And then there are those that don't even have the key and Steam installer.

Really? Isn't that just a poster then?

The Battlefield 1 Collector's Edition pack was sold in a few different configurations, not all of which included the game.