Tandy makes a product called "Saddle Lac" that is a spray on laquer. If your leather bag is fairly stout and doesn't bend much, it will work great. If the bag is somewhat lightweight and can bend and crease easily, the Saddle Lac will crack at the bends and peel off. Simply warm up the can (place can in a ziploc bag and run hot water over the bag), then shake it like a rattle paint can, and spray a light coating over it.