I have two tools that I've found really help my gamedevving in general:
Notepad++ is great for those occasions when I need to look at something's source code but don't want to open a big heavy IDE to do it (and even something like Atom or VS Code is heavy in comparison). Also helpful for when I already have a big heavy IDE open but want to look at some other project's source code.
SpeedCrunch is the next best thing to just typing math into a python shell. It's a powerful calculator with a visible history and can even have variables.
What shortcuts are you forgetting for Gedit? They're exactly the same as just about every other simple text editor. If you're looking for a fully featured code editor, why not use something designed for that like an IDE, Vim, Emacs, atom, kdevelop, qt creator, etc? Here we're talking about the most basic text editor... You'll notice that all the productivity software works exactly the same as it always has.
Edit: Check out pluma.