Oxa Home via Amazon offers Prime members its OXA Hydration Backpack with 2-liter Water Bladder in Blue or Black for $25.99. Coupon code "FG5QAGZQ" cuts that price to $18.19. With free shipping, that's $22 off and the lowest price we could find. It features adjustable shoulder straps, a BPA-free 2-liter water bladder, and thermal insulation layer.