To see an interview with Ruth Warrick, who played Kane's first wife, insert disc one and go to the special features menu. From there press the right button on your remote control and then press the enter button when you see the highlighted sled.
To find a hidden interview with the movie's editor Robert Wise, choose the production notes option and then "on the set". Next select "News on the March" and then click the up button on your remote control. When you see another highlighted sled, press the enter button on your remote.
All easter eggs were generously submitted by Bjorn_K