This pillow isn't very compact, it will still fold down and fit in a backpack, but it's the only way I've been able to sleep on a plane: https://www.amazon.com/Inflatable-Airplane-Comfortably-Airplanes-Drawstring/dp/B083NVHN13

For the aisle, I put the tray table down and lean my face into it. For the window, I slip an arm through the hole and lean left or right.