In a very large skillet cook ground pork, sausage, pancetta, onion, and garlic over medium heat until meat is brown and onion is tender, using a wooden spoon to break up meat as it cooks. Drain off fat.
In a 3-1/2- or 4-quart slow cooker combine meat mixture, carrots, celery, and sweet pepper. In small bowl combine wine, tomato paste, salt, thyme, and crushed red pepper; add to cooker.
Cover and cook on low-heat setting for 6 to 8 hours or on high-heat setting for 3 to 4 hours. If using low heat; turn cooker to high-heat setting. Stir milk and parsley into cooker; cover and cook on high-heat setting for 20 minutes more.
To serve, use a slotted spoon to spoon meat mixture onto roll bottoms. If desired, add desired toppers. Cover with roll tops.