Emacs: Enable narrow-to-page.
Emacs: org-narrow-or-widen > narrow-or-widen-dwim.

This has at least one more use case, where I've selected a region.
Emacs: Add extra binding for Smex.
Emacs Org-Mode: Add smartparens formatting pairs.
Emacs Org-Mode: Add and bind org-go-speed.
Emacs Org-Mode: org-down-element speed command.