If you're going light and fast—trail running, mountain biking, or backcountry skiing—Ruffwear's Singletrak ($90; ruffwear.com) is the pack for your pooch. With two pouches that have a carrying capacity of 2.4 liters (in small, medium, and large), the lightweight, breathable pack keeps the load high and tight on the dog, which makes for comfortable, easy movement. Plus, the Singletrak comes with two .5-liter Platypus water bottles—one for you and one for the dog. The only disadvantage is that if you need more room than to store the bare necessities like a few treats, a leash, and a poop bag, the pack might not have the space. If you're looking for a long-haul pack, Ruffwear's Palisades ($125) has two removable saddlebags, a two-liter hydration system (complete with a hose for filling a dog bowl), and a load-compression system that keeps the bags close to the dog's body. With this 13-liter (medium) pack you can load up Fido for a week in the backcountry and he'll barely feel it.
If you're looking for the Mac Daddy of doggie bags, try Granite Gear's Rough Rider ($50; granitegearstore.com). With a carrying capacity of 18 liters (medium), your dog can haul a lot of extras, like your rain gear and a post-hike beer, without getting bogged down. Don't feel bad about sharing the load: Dogs can carry 25 to 30 percent of their body weight. Plus, the pack has fleece-backed foam pads that will make it feel like it's floating on your dog's back.