CamelBak's minimalistic Classic pack has what you need for no-hassle, no-hands hydration. With 2-liters of fluid capacity, the Classic holds the equivalent of three water bottles. You can also store your keys, cash, and an energy bar in the secure outer pocket. The reservoir is easy to fill and clean, and the breathable mesh harness allows heat to escape so you stay cool.
For fast getaways and easy refills, this pack sports CamelBak's External Fill feature. It's a wide, screw-on top that lets you fill the bladder without having to remove it from the pack.