The Express Access does not apply to City walk. I think most of the restaurants will except ressies which can be made before going to the parks. There used to be a booth close to Margarittaville that made ressies.
Our room key from the HRH got us right into the HRCafe. When we went there were long lines to get in. We just by-passed the check in person and went right to the door and showed our key. We were seated in five minutes. There are several restaurants in which your room key will get you "next available seating".
The only Citywalk restaurant that I know of that doesn't do next available seating is Emeril's. You need a reservation months ahead of time to get in there.