Last week I flew back from SYD and noticed the person sitting across the isle from me pull a folded up mattress pad out of their backpack and put it on the seat. It was pretty thin and it looked like it fit just right except it was a bit wide where your feet would lie. I didn't want to ask how well it worked.

Because I was curious I searched a bit on the internet and found this at REI.

LINK

I've never seen anyone do this before. It doesn't look like much padding for the trouble of lugging it along. I don't think I could ever use one, unless the comfort was unbelievable, because I hate calling attention to myself. I would have to guess this person flies this route, or other similar long hauls frequently to make this worth it.