Inov-8 Race Pro Extreme 4

A hydration pack should carry water and stay out of the way. This does just that, with space for a few essentials like a shell and a snack. Weighing just 11 ounces with room for 2 liters of water in a horizontal bladder that doesn't bounce, it's great for trail runs, scrambles, or even stuffing inside a bigger pack for summit attempts. [$150; inov-8.com]