USB drives are a cheap way to store lots of stuff. Some even come with built in encryption (Sandisk for one), so if you lose it, it will be hard for someone to read your files/data/info. They may not be as fast as cloud storage, or some of the high capacity external hard drives out there, but for my purposes, they work fine. They serve the backup purpose well.
I have 3 X 128GB Sandisk drives, self-encrypted, and can back up around 70 GB of personal data in around 2-6 hours. It varies depending on whether or not I defrag the hard disk first, or encrypt the data first, before the Sandisk encryption kicks in, which seems to affect the data transfer process. I do it every once in a while, maybe monthly, and rotate through the 3 drives, overwriting the one with the oldest data (like GDGs in MVS O/S).