POP-I's E Ink backpacks use an E Ink panel on the back. You can customize the image via an application on your phone (iOS or Android). There are several backpacks available, with a display size of either 4.7" or 10" (HD). The bags themselves are made from either canvas or leather.

POP-I E Ink backpacks photo

POP-I said it was to ship those bags at the summer of 2017, for $99 to $399.

E Ink display info: 
4.7" / 10" HD E Ink


a good option for advertizing

E-ink backpack will be a good option for advertizing,
especially in stations, malls, etc.