Lets see....
Low vis...allowed, even CATII/III.
Rejected takeoff...Captain ONLY.
Landing on contaminated runways/windshear...Captain normally allows, no company restrictions.
Circling (we are category D), yes, the First Officers do it all the time where we fly. Standard ops.
Taxiing?
No, no tiller on their side.
Signing the tech log?
Nope, not allowed. Captain ONLY.