I used to be able to sleep anywhere, anyhow, with a pack or helmet for a pillow... no more. I'm well past the age where I can go to bed fine and wake up injured... it's happened! And then it takes a week to get that kink out of your neck and back. A good pillow is no longer a luxury item while camping.
Years back, in my late 30s, I just used some spare clothing in my sleeping bag's stuff sack and called it good. I even made a silnylon bag with a piece of fleece on the side for this (still use it, but with an air pillow). I moved off the ground into a hammock in my early 40s and discovered that my neck placement needed to be different, and bought a cheap self-inflating air pillow that weighed about a half pound. I eventually ponied up and bought a Sea to Summit Aeros at 3oz or so and have been very happy with it. Well worth the cost. I like that you can adjust the thickness with the amount of air. Inflates easily.
On the ground, I usually take my shoes and put the heels together, spread the toes open a little, and set them under my head under my groundsheet, then use the air pillow on top, as normal, and it gives me a little extra boost in height not needed in the hammock. Sometimes I use a piece of split firewood or a rock or two to keep the shoes from sliding away from me.