What does more of gravy than the grave mean?

I believe that Scrooge is telling Marley that he is really a figment of imagination due to his upset stomach than the acceptance that Marley is really a ghost. In Dickens book "A Christmas Carol", before going home after work , he stops and eats at his usual pub and when he arrives home, Scrooge eats some gruel before he is about to go to bed, because of his upset stomach.