For outdoor recreationists, water is essential—for cooking, for cleaning, and to keep ourselves and our furry friends from dehydrating. But water is also heavy and takes up space, especially on longer backpacks. With that in mind, I decided to start carrying a filter—something that would be light in my pack and easy to use on the trail. The Autoflow Gravity from MSR solved all my problems at once. At less than a pound, it’s much lighter than a couple Nalgenes, and it uses gravity to filter water from its four-liter reservoir to your bottle or bladder. With such a large filtration capacity, this is a great product for folks who tend to hike in groups. Available at Bob Ward's and Timber Trails. $120; msrgear.com.