Sometimes in extreme situations small things can make a big difference. Exhibit A is the Therm-a-Rest Trekker Pillow Case, a soft fleece pouch that you can stuff full of clothing to make a field-expedient pillow. And at only 2oz to boot.
This little item went up Denali with us last season and turned out to be a great piece of kit. It doubles as a stuff sack for all kinds of clothing, in our case expedition weight base layers. We just pulled it out at night, threw it in the sleeping bag and laid our weary heads to rest. The 14×17 inch size will tuck in nicely to most bags, and a foldover flap keeps the contents in.
It's more than just a creature comfort. A good night's sleep is a safety and health issue on a big mountain. If you're carrying a stuff sack anyway might as well make it do something else while it's along for the ride. Another nice function is it keeps all your skull-nastiness away from your sleeping bag, keeping it cleaner. Nothing quite as nasty as a bunch of brain fungus contaminating your expensive down fartsack.