During transit: No bare hands-operation
Zoom in / out
Pan
Toggle between different modes of navigation display (map - arrow showing direction to next waypoint, )
Set wp at my position (and preferably give it a name that makes sense)
show/hide my track

Preparing transit: (Preferably done somewhere quiet, where I can consentrate. Normally, I'd do this stuff with bare hands).
Prepare waypoints (from coordinates, or by clicking in the map)
Map display - to familiarize with route, and how the GPS map will display the terrain.