Walmart offers the Stanley Adventure Series 5-oz. Pocket Flask for $10.99. (Amazon charges the same with free shipping for Prime members, however it's temporarily out of stock. It can, however, be ordered at this price for delivery when available.) Opt for in-store pickup to dodge the $5.99 shipping charge. That's the lowest price we could find by $4. It features a leak-proof cap and single-wall insulation.