You tend to pay more to carry less in the rarefied class of one-pound, down summer sacks. That's why the barely-over-a-pound Flash is such a surprise: For packability, weight, and warmth it rivals bags that cost much more. And there's nothing cheap about its silky shell and 750-fill feathers. A three-quarter-length zipper and narrow cut keep weight down but restrict roll-around. 40°F, 1.2 lbs; rei.comBonus: Compresses smaller than most down jackets.Bummer: The nylon shell isn't particularly water-resistant.