Gonex via Amazon offers its Gonex Ultralight 20-Liter Travel Backpack in Rose Red for $9.98. Coupon code "E8B8CJH8" cuts that to $7.98. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $5.58.) That's the lowest total price we could find by $2. It folds up into small pocket (sandwich size) and is water resistant.