Whether you are car camping or backpacking, or, a long day hike where you are looking to take a rest, you already have a pillow with you. There is no need to take an actual pillow (way to big and heavy for backpacking!), or even one of those smaller travel pillows.
All you need to do is take a stuff sack and stuff it with anything fluffy, like extra clothes, jacket, etc., and there you go, a pillow!