As with a human, a dog needs fuel and water when out running. I could carry it for her myself, but I started to look into options for what was out there for dog packs, and came across Ruffwear (www.ruffwear.com). I contacted the nice peope there, and they were good enough to send me their Singletrack Pack (http://www.ruffwear.com/Singletrak-Pack-Dog-Pack) to test out and review. If you run or hike with your dog, check out their site- they have a lot of really good gear on there.
The pack has a sleek and close to the body profile. It's not made to hold a lot of gear- just the necessities for a long day out. It has 4 small pockets, two of which contain soft sided water bottles. The other 2 are each big enough to hold several cups of dog food, poop bags, or whatever ever other small necessities you might have. It small enough too that it doesn't restrict her movement or throw her off balance. It seems like once we get going she forgets she's wearing it.
Percy wasn't too excited to wear the pack at first, but it didn't take long for her to realize that whenever she put the pack on it meant we were going for a run, so now when she sees me reaching for it she gets excited.
This pack is going to be an integral part of the adventures that Percy and I will have together, and knowing that we'll be able to carry all the fuel and water she needs is really nice.