For the display, I would love to re-create Professor Steven Mann's EyeTap, but the optics are beyond me. Instead, it would be easy to start with TV glasses and perhaps take them apart and find a better long term mount (e.g. in a hat). Eventually that could be upgraded to a small LCD displays if the optics could be worked out. (see the inspiration links)

An app on your cell phone would BLE data to the display and receive back head tracking data so that it could react to head movement. GPS from the phone would allow e.g. arrows for directions.

Or you could just use the phone for it's connection to the internet, and do all the apps on the Pi Zero itself.

With a portable keyboard / mouse, you might be able to work while strolling through the park, or be connected 24/7 even when at social functions.... which is every cyborgs dream.