I've seen jackets with built in iPod controls [1], cycling bibs with iPod controls [2] and even some traditional Lederhosen with not-so-traditional iPod controls [3], but I've never seen a backpack or bag with simple iPod controls on the strap.

The iPod Mono Strap Backpack [4] allows you to store your iPod inside the bag's duratex nylon exterior, while controlling the five button ElekTex Smart Fabric control panel on the strap. It costs $89.99.