Delta Cycle Expandable Mega Wedge Bike Seat Bag for $9.93. Select free ship to-store for in-store pickup at REI. Otherwise shipping is $5.99, making the total $15.92 shipped, or, shipping is free for REI members on orders over $75.00. Here is a screenshot for your reference. It features expandable wedge bag with velcro attachment to any seat, hi-visibility expanding compartment, see-through top compartment, and reflective webbing for added safety. Most places have it for about $21.