USFS 1 Quart Canteen. Perfect size, cheap canteens.
When going longer distance you want to have more water. 2-3 Quarts at least. Light and inexpensive, 2 of these are under $12, and plus a water bladder, is 3-4 Qts right there without sacrificing weight or structural integrity. Their unique shape being more square instead of round takes up less space than a circular bottle and thus more efficient to pack