During fashion week last month, I noticed that many designers — including Stuart Vevers at Coach and Pierpaolo Piccioli at Valentino — showcased single-flap shoulder bags alongside more statement-making accessories.Though not quite as show-stopping as oversized totes and feather-embellished clutches, a well-designed flap style is the backbone of any good purse wardrobe. It makes for a great everyday handbag since it can be worn on the shoulder or crossbody, and often fits more than just your wallet and keys (you’ll have to carry an extra tote for your work-lunch and coffee thermos, unfortunately). And, depending on the material, many styles have a seasonless appeal and can be worn year-round. (Although, in fall and winter, it's best to stay away from bags in linen , clear plastic or natural materials such as wicker and straw, they might feel too summery.)Here are three stylish (and on sale!) leather shoulder bags that you’ll want to wear all through autumn , and beyond.