Crab casserole is a baked dish and is baked to more or less of a moist finish depending upon preference. Crab casserole is generally kept a little moist and soup along with milk is generally used in the preparation to keep it moist while baking. Mushroom soup is the most commonly used ingredient but sweet corn or vegetable soup could also be used. Mayonnaise, cheese, bell peppers, milk, eggs, onions, celery, salt and pepper are the basic ingredients in the crab casserole.