We like to head out for a quick after-work run, hike, or bike ride with the minimalist Camelbak Hydrobak Light Hydration Backpack. This lightweight pack carries a 1. 5-liter Crux reservoir to keep our fluid levels up over the course of a 1. 5-hour ride, while its external-fill reservoir opens wide, closes with a snap, and lets us reload water without unloading the pack.