One thing I've really liked playing with, recently, are sessions. Usually sessions are desktop environments, but you can make dedicated custom sessions for specific software. That way you don't start any programs you don't need. So you can save the resources you would normally use for the window manager, update checker, etc.alj said:
With a bit of scripting, you can actually make your own console-like sessions, even making it controllable by a gamepad. It's fun stuff.