REI Garage offers the Timbuk2 Medium Strap Seat Pack in White or Diablo for $10.73. Opt for in-store pickup to dodge the $5.99 shipping charge. That's tied with our mention from last August and the lowest price we could find by $7. It measures 6.5" x 3" x 2.2" and features a keyring tether, hook-and-loop strap, and durable ballistic nylon.
Crocs via eBay offers the Crocs Unisex Modi Sport Realtree Max-4 Flip Flops in Chocolate/Khaki for $22.99 with free shipping. That's the best price we could find by $9. They're available in select men's sizes from 4 to 15 and women's sizes from 6 to 10 12.