What solutions have you guys been using for storing all of your DRM-Free backupos? I plan on getting at least a 1TB USB 3.0 external HDD for GOG and Humble Bundle stuff I've been hoarding on my HDD which is quickly running out of space.

Moving data to an external drive is not a backup. Backup means duplicating.
So if you want to do the backup thing while freeing up space on your internal HDD; get at least 2 external drives.

I have an 8 TB USB3 drive; A few Syncback Pro profiles running daily to back up (changes to) my internal drives. Yearly I do a manual copy to a pair of offline 2,5 inch USB drives.

Technically, I already duplicated the files I am entitled to that are stored on GOG's and Humble Bundle's servers to my HDD so they are indeed backups by your definition. In the event that I loose internet access or definite access to my accounts, they are backed up to local HDD.

But if your HDD fails, you can't download older versions of GOG installers anymore (you might not be interested in that... but it's a thing).

Anyway, I consider cloud backup as an extra, next to local duplication. If anything happens, I want to be up and running again as quickly as possible. But that's just me.

I see what you're saying. Never though about actually backing up older versions of games unless I was aware of a drastic change between them; currently I know of none. At the moment, I am strongly considering docks or enclosures for my HDDs that are lying around unused [except for having non-dual boot OS' just in case].

Otherwise I'm going for dedicated external HDDs from one of these two options since it's less safe transferring around naked HDDs.

Toshiba 2TB
https://www.amazon.com/dp/B079D3D8NR/

Western Digital 2TB
https://www.amazon.com/dp/B07VTFN6HM/

I'm currently using two external 4TB drives, one of which I'm downloading any updated installers to. The other gets synced to the main drive every month or so.

Backup should be at least two different things. You could use online account as second, but loss of connection is a problem. This is my setup, and is a bit overkill:
Main pc, has 3 hdds striped as one drive.
4 * raid boxes setup as raid 5 so one drive redundancy for drive failures, all clones of the main machine. 2 onsite, 2 offsite to cope with disasters.

You can get away with smaller drives, but do be aware, once you start storing things, it rapidly increases. Data will for the foreseeable future exponent in size. I would go for 2 of what you can afford.

Also, think carefully how to store things will save you considerable time later on. At first I just dumped things on a drive. Later on I had to manual reconfigure that which took ages. A good consistent approach means you can automate these things, my folder setup is:
<series>\<game>\
Or
<game>
With subfolders:
Docs
Mods
Patches
Saves

With this i can simply script moving or changing of this setup, or check it.

And finally, if you want to track what you have, use a proper database, or some software like collectorz. It’s highly likely if you use excel that it will go wrong at some point, sort especially.

I need any solution I decide on to be portable and USB3.0 without external power if I can help it. I wouldn't mind carrying around a 3.5" in an enclosure even though it'd be a bit heavy. Don't really have a need to have a stacked storage enclosure at the moment but thanks for reminding me that's an option.

Don't all 3,5" enclosures need external power? I should look it up, but that's how it was the last time I searched for one...

The organizing aspect is definitely not overkill. I know I've downloaded mods twice and upwards because I forgot I abbreviated the game it was for at one point and then decided to write out the whole name because I kept overlooking it. Since these drives are strictly for backing up my GOG and Humble Bundle DRM-free stuff, I'm also gonna get another one for media and will take into consideration of getting two of each but I'm gonna be strapped for cash in the coming months cause of the holidays. Speaking of which, I'm gonna scope out black friday deals for storage.
This was the typical case but I think USB 3.0 has enough bandwidth to power it up if I'm not mistaken, otherwise gonna wait for black friday and look at newegg or similar stores.

Sure. These are quite good from experience as small, usb powered, high capacity external drives:

https://www.amazon.de/dp/B0713WPGLL/ref=sr_1_3?keywords=4+tb+wd&amp;qid=1573333297&amp;sr=8-3

I have a 2fb one, a 4tb one, and the partner has a 2tb one. They are nice. Definitely wait for Black Friday sales!

Have you ordered them from the link above? If yes, I'm surprised they arrived intact - I'd be wary of ordering electronics from Amazon, given how they treat the packages. When I was ordering books from Amazon UK, one of the books' top of the spine was slighty dented upon arrival due to mishandling of the packaegs. A few millimeters, not much, but still - if they were moving them with care, that wouldn't have happened.

I've been thinking of getting this one as well, eventually, and they say that the bigger sizes are still PMR, which would be great since I want to use mine to watch videos and use for games - emulators, and supposedly SMR isn't good for that, just archiving.

Edit: WB Elements have great reputation and are topsellers.

I didn’t get them from the german site, but the uk one. And they turned up fine in a further cardboard box. In fact amazon mostly puts too much packaging on. The delivery person is what you take the gamble on, I have had beer deliveries when I am away left outside the front door, and things thrown over the back gate.
Generally performance seems fine. It’s usb 3 so reasonable speeds too.

I heard that your average external drive cannot be uncased and inserted in your PC anymore?

I used to do that because when an external drive failed, i could uncase it and install it in my pc and it worked just fine. (Something about external drives made them want to f--k up but actually the HDD still works just fine)