This travel daypack zips up into a tennis ball sized bundle

On my last trip to Tokyo, I brought along the Sea to Summit Ultra-Sil Day Pack ($26.99 on Amazon). It weighs 2.4 oz (my iPhone 6 Plus weighs 6.2 ounces) and zips up into a bundle smaller than my fist. But it holds 20 liters of stuff, and I used it every day to carry water, snacks, sweaters, an iPhone charger, a portable wifi, groceries, and things Carla and I bought while walking around. The material feels indestructible.