Action Bar Pager

Keybindings for temporarily switching action bar page on key press, then back on key release. See screenshot for keybindings.
This is extremely useful and allows you to use any button like a quasi-modifier (like shift, ctrl, alt), including mouse buttons.
You can bind for example MOUSE4 or MOUSE5 so that they switch to different action bar pages when you hold down the button (and then switches back when you let go).