Walk into any running store and you’ll find hydration packs covered in zippers, tubes, pockets, and straps. They look technical and promising. Many runners buy one, take it on a long run, and end up hating it.The problem isn’t the pack itself most of the time. It’s that most runners shop for hydration packs the same way they’d shop for running shoes or a new phone. They read reviews, compare features, and pick whatever sounds…