When working on something important and can't afford to lose everything you've done in case you accidentally do something that erases your work, the file containing it gets deleted or becomes corrupt, your computer crashes or something wrong just happens.

If yes, where? Compact discs? Removable media? Cloud data? Or do you just make a new copy of the file?

Nope

In fact I'm doing the opposite today and never showing up again on no notice

Google Drive I guess. I have an external hard drive I save photos to sometimes [on top of Google Photos backup]

No, and thinking back now, there were a few times where it could have ended disastrously

I had to type a 60+ page project one time, and I was doing it on a pretty old computer, and not once did the thought of ever backing it up even cross my mind.

If the computer had crashed, lawd

I always upload it on my gmail I'm too paranoid

me too, with every few lines completed, I upload again it to Google Drive

Yes. Mostly by email or USB.

Google Drive.

Everything I save in my computer, I also save it in my Drive.

Of course, I'm not an idiot.
Google Drive

Since the flash drive where I had all data and files of the first years of my degree randomly died I back up on multiple devices. I lost absolutely everything

Sometimes when i'm really hot and sweaty

Yeah Onedrive

like what? a document? google docs saves it for you like this

Sometimes when it's really important. But I've been too paranoid, I even made my own gmail for sending it not only on my own, but also to another email. If it's too heavy- cloud or removable media.