I’m a reformed marathoner, but I still like to road and trail run. The right pack makes it even more enjoyable.
For a long day of running, you want something light and comfortable, with just enough capacity to keep you hydrated and fed. Something like the CamelBak Marathoner Hydration Vest ($100). It’s a light, sleek pack that stays close to your body. It can carry 70 fluid ounces of water, and the CamelBak Big Bite valve makes it easy to get a drink. Cargo pockets hold a cell phone or gel packs, and a mesh pocked can carry a light jacket or vest.