Originally Posted by augkor

I have used this Therma-rest cushion on many international flights and long domestic flights. It is the best thing I ever purchased for long flights in economy.

Amazon.com : Therm-A-Rest Travel Cushion, Nautical Blue : Sports & Outdoors

It is also very small once the air is out of it--you can either roll it up or fold it in half. It is self inflating and once the air gets in it you can use the valve to adjust the amount of air to make it more comfortable. You place the cushion with the curved part toward the back of the seat and it takes the weight off your tailbone.

I noticed that Amazon is backordered, but I'm sure you can find it online somewhere else.

Highly recommended if you want seat comfort and you pack light.