Wolfyok via Amazon offers its Wolfyok 20-Liter and 10-Liter Roll-Top Duffel Dry Bag in Yellow for $9.99. Coupon code "MT3BOY23" drops it to $7.99. Plus, Prime members bag free shipping. That's $6 off and the lowest price we could find. (For further comparison, we saw a 2-pack for $18 in August.) This waterproof PVC bag features a removable, adjustable shoulder strap.