Pound steak to 1/8-inch thickness. Combine apple, breadcrumbs, onion, celery, salt, and sage. Spoon stuffing onto steak, spreading to within 1/2 inch of edge. Roll up jellyroll fashion; tie with string to secure stuffing.
Brown steak roll on both sides in hot bacon drippings in a Dutch oven. Add hot water and vinegar. Cover and simmer 45 minutes over low heat. Turn steak roll; add prunes, and simmer an additional 40 minutes or until steak is tender.
Remove string. Place steak roll on a serving platter; spoon prunes around steak. Pour gravy over steak; slice and serve.