As a US certificated commercial pilot with an ATP, no I can't tell you what 91.103 is off the top of my head. However I tell *every* pilot that is trained at our company "don't memorize regs by number". There is one easy answer on every oral - "I don't remember exactly but I know where to reference that."
I admit I looked it up and that regulation is actually superseded by regulations under FAR Part 121. The preflight is replaced with the requirement of the aircraft to be in an airworthy condition with all records reflecting such as per FAR 121.303 and FAR 121.605, weather requirements are covered by FAR 121.599, FAR 121.99, 121.103, and FAR 121.607 cover the need for navigation facilities for domestic operations, FAR 121.189 and 121.195 cover performance requirements and weights, and fuel requirements are set forth by 121.639 for domestic operations.
Commercial aircraft are not required to carry the POH or AFM if the operator has an approved FCOM. In other words air carriers are authorized to develop and author their own versions of the POH/AFM so long as it is approved (or accepted, I can't remember) by the Administrator. The FCOM is not required to have landing/takeoff information if the operator has an approved Airport Analysis manual available to the flight crew.
So in short, no - I don't know 91.103 and it does not apply to my operations.
If that is the regulation you think drives requirements udner FAR Part 121 I would call into question your air carrier training.