Place all ingredients except the rice or lettuce leaves into a large plastic food storage bag. Seal the bag well and place in the freezer. When it comes time to cook, thaw overnight in the refrigerator, and empty the contents of the bag into a 4- or 6-quart slow cooker. Cover and cook on low for 7-8 hours, or until the meat shreds easily between two forks. Shred completely and serve over rice, or stuffed into large romaine lettuce leaves.