This 15-inch MacBook Backpack also has a USB port to charge a device: $15 (Reg. $30)

$15

SosoonDirect (98% positive feedback lifetime) via Amazon offers its 15-inch Laptop Backpack with USB charging port for $14.99 Prime shipped when code BMHSBJOS is used at checkout. Normally $30, this is the lowest we’ve seen it offered for and the best available. Though Sosoon includes a Lightning cable, we cannot verify if it’s MFi certified, so we recommend picking up a known good cable to use with your iPhone. Rated 4.2/5 stars.

Sosoon 15-inch Laptop Backpack features:

• Anti-Theft: The hidden zipper and invisible pockets located on the back keep your laptop and other valuables safe and handy
• External USB Interface: You can easily and conveniently charge your phone, tablet and other devices without opening up the backpack
• High-Quality Material: Made of water repellent, tear-resistant and anti-scratch oxford fabric for lasting durability
• Multi-Compartment: 13.5″x 6″x18″ (L*W*H). Generous main compartments with a padded sleeve for 15.6-inch laptops and several functional pockets allow you to keep all of your gear secure and organized in its place
• Comfort: The innovative weight balance design makes you feel 20%-25% less weight. The body side and shoulder straps have excellent thick breathable mesh padding, offering your back plenty of cushioned comfort