For me, my high bar that I have yet to beat, was the time I pivoted the running OS (ubuntu) into RAM over SSH so I could unmount and image the boot drive without rebooting and loading a live USB (Which would have required a ticket with my provider to enable IPMI)
2 that stand out to me:
When I successfully got virtualbox to boot my windows xp partition inside Linux because I needed to run some software for school.
When I figured out how to use qemu-nbd to mount a qcow2 image backed by a physical block device in order to run non-destructive filesystem repair and file recovery with test disk. Did that for a while for my university IT help desk to quickly save files off failing disks.