I've repurposed a 32 GB M.2 SATA SSD as a bootable "USB stick" and I'm putting useful tools on it. So far I've got memtest, seatools, gparted live, system rescue, clonezilla, and a live install iso of the distro installed on my PC. What other great bootable tools am I sleeping on?
Not spesifically a tool to put on a USB stick, but Ventoy is worth checking. I've had a bit mixed results with it on older hardware but when it works it's pretty easy to manage your carry-on-tools.
Testdisk, clamxTK, rkhunter or chkrootkit, mobile verification toolkit, lshw, time shift maybe deja-dup.
I think your idea is a good one. Like a linux Swiss Army knife. You can have lots of tools that you don't need all the time but might be handy in a pinch. Especially if you don't have internet.
Testdisk is great. I recently cleaned a drive with diskpart and after the initial 100bpm "oh shit, wrong drive" moment, I fixed the partition structure with testdisk. Took a while, but pretty simple and easy to use.