Dark green nylon rain covers for some of our past and current bags.  Not An Absolutely Necessary Item since the cotton canvas duck and tweed materials we use for our bags are already extremely water resistant But these covers are very nice Peace of Mind products if you're carrying around sensitive electronic things.

Elastic draw string cords, hook and loop (velcro) closures, and leather patch reinforced openings mean these rain covers will last a lot longer than the makeshift plastic breadbag thing you're using right now.

Weighs practically nothing, scrunches up to super small so just take it off and keep it inside the bag for the bright and sunny days.