What are your most favourite editor shortcuts?

You can copy and paste text by selecting it and pressing CTRL+C to copy it and then CTRL+V to paste it. It's my favorite.

For standard CUA editors: Control + Shift + Arrow-key to highlight words.

But I use Emacs so everything I do is a shortcut. Maybe my favorite Emacs shortcut is actually a short-cut framework called Hydra. You enter a temporary state where all key-bindings are shadowed with custom bindings, allowing single key presses to perform anything.

Vscode (and others): cmd+shift+f to search in files, and related shortcuts to navigate through the search results and quickly open the matches files. I use it literally hundreds of times a day often with regexps, especially in projects with several heterogeneous files (scripts, makefiles, Kubernetes manifests, ...). If I had to reach the mouse every time I do a project search, my productivity would plummet.

On a more meta, cmd+shift+p to open the command palette so I can execute commands by fuzzy matching, so you can do some random actions without having to navigate the UI manually (typical things I do could be view git log, stash something, stage a chunk of the file, ...).

Intellij's Alt-J (multi-select) and Ctrl-W (progressive select) are the most productive for me.