When I’m out for a hike I happily swing my biggest Nalgene loop-top bottle, but back in the city I just don’t need to hump that much water. Instead I just slide a slim Nalgene flask into my bag. The slightly curved profile is reminiscent of classic hip flasks, and an insulating outer sleeve slips over the 12-ounce, taste- and stain-proof polyethylene bottle. The 1-ounce shot cap snaps on over a twist-on leakproof lid. What would you fill your flask with?

Nalgene Flask, $6.95

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