TomTop offers the Tomshoo 30-Litre Ultra Lightweight Foldable Backpack in several colors (Blue pictured) for $7.69 plus $2.65 for shipping. That's tied with our February mention and the lowest price we could find by $3. It folds into a zippered pocket.

Note: It's available shipped from the China warehouse for $9.99 with free shipping, but it will take two to four weeks to arrive. Also, the countdown timer on the product page does not reflect an actual expiration time and resets daily.