The Bike Shopper bag is similar to the Ortlieb Backroller Classic panniers, except slightly smaller and comes as a single bag.  Perfect for people who want a high quality, waterproof pannier but don't need a pair of them.  Comes with a unique slide-lock closure and two carrying handles that double as a shoulder strap.  Ortlieb's QL2 mounting system makes configuring this pannier to your rear rack a cinch!