Preheat oven to 350 degrees F and lightly grease an 8 inch baking dish. Combine the corn bread, toasted bread and crackers in a large mixing bowl. Pour the stock into a saucepan and add celery and onion. Bring to a boil and cook for 10 to 15 minutes. Remove the stock mixture from the stove and allow it to cool for about 10 minutes before proceeding. When it has cooled, add the stock mixture to the bread crumb mixture along with the eggs, butter, sage, and salt and pepper. Mix well.
In a skillet, saute the onion in the olive oil until it is brown. Add the butter and lower the heat. As the butter melts, add the flour, stirring constantly to keep it from burning. After the flour browns, add the stock and stir until the gravy thickens. Season with salt and pepper.