And if it doesn't fit in the pocket, it also has loops and straps so you can attach it to the tray table or seat. Plus, it has five interior pockets, a Smartflap for your phone, and a crossbody strap to carry it easily when not on the flight.
Promising review: "I bought this seat back organizer specifically for an overseas flight to Europe. I LOVE sitting in the bulk heat seats but hate the fact that there is never anywhere to put all the stuff I need for the flight. I was pleasantly surprised how much this holds. It may appear to be thin, but it really expands to hold a lot of stuff. I had my iPad, headset, chargers, hand lotion, chap stick, passport, etc. right in front of me the whole time. And BONUS, it even was wide enough at the top for me to put my water bottle! This worked through the airport as a 'purse' and then worked fantastic on the flight. I highly recommend this for air travel!." —HRHJennyJ
Get it from The Container Store for $59.99.