Move all lines matching pattern to start of file

:g/pattern/m0

Revert to previous versions of file

May depend on your undo settings

:earlier 5m  " revert to version 5 minutes ago
:earlier 2f  " revert to last save before last
:later 1h  " revert to 1 hour later version

Show lines containing “this” but not “that” or “the other”

:g/this\C/v/that\C/v/the other/#