For work, it's my bespoke spreadsheet that automatically calculates when and how much I need to have on hand for any particular item. Our system is technically able to do this, but no one has ever turned it on, so I created one myself in order to get my inventory under control.
At home, it's probably the blender file of my current project for X-Plane that represents roughly a year and a half of my life so far. I have backups in multiple places of course.
I do something similar except I have my own cryptic way of writing my passwords that only I understand. I will never trust an outside source with my passwords ever. EVERYTHING gets hacked at some point...
Going back to default tmux feels so wrong. I've got a bastard config that comes from muscle memory from starting with GNU screen with a dash of i3 sensibilities
Not a single file, but a folder with mementos associated with someone who has been a really good friend to me for the past two years. Said friend also has a folder for saving the stuff I send them, so it's mutual!
I keep my passwords and other sensitive information in a written diary, you never know if you might get hacked, so I took that precaution.
Nearest thing I can think of is a running file with medical guidelines I use occasionally but not often enough to want to learn, childhood vaccination schedules, colonoscopy follow up timelines, lots of imaging follow up guidelines.
I know some nurses that know them pretty good, it's not that outrageous to know the schedule by heart if you use it most days. I don't use it most months though.
Not including work devices - probably my old university files. I intentionally wrote about topics relevant to the career I wanted (which I now have) and they're genuinely useful for going back and referring to.
The one containing all my ID information and passwords and stuff. I have at least six replicas of it, tactically hidden in places where I'd find it but nobody else can, similar to the five rings from Captain Planet.
Yeah, but the infinity stones are at least useful individually. You need the five Captain Planet rings for anything resembling their main purpose to be possible.
My most important file is an insanely customized, self-compiled binary on Gentoo, embedded with multiple layers of encrypted payloads—using a hybrid of AES-256 and RSA, stored in a hidden LUKS partition on a remote server. The entire setup is wrapped in a fortress of security-hardened CFLAGS, with each layer only accessible via a complex, time-sensitive keystroke sequence using a YubiKey. The system is so finely tuned that it only runs on a specific kernel version optimized for speed and stealth, pivoting through an ever-shifting network of proxy chains. If anyone tries to tamper with it, the dead man's switch wipes everything in an instant. Good luck finding it OP.