Add the shortening to a heated skillet, once melted, sift in flour to make a roux. Once deeply browned, add in the onion, bell pepper, celery and garlic. Simmer until wilted. Move to a stock pot with the chicken, sausage, okra and tomatoes. Add water to suit and a capful of the crab boil, along with the salt and pepper. Cook until tender. In a separate pot, cook the shrimp with crab boil according to directions. Once the chicken is tender, add the shrimp and cook for 15 more minutes. Best served plain or with rice, and gumbo is always better the second day.