Fastest, easiest, cheapest, maybe lightest DIY pillow:

Recycle Tyvek mailing envelopes into a stuffsack/pillowcase. Insert a reclaimed/recycled mylar balloon and inflate it as desired. You will need a straw and something to keep the balloon closed. Stuff a down sweater around the balloon. Close the bag. By day, use the stuff sack to hold night needs, maybe the down sweater. I used to carry a silk outfit as town/camp/sleep clothes. This was when silk was more commonly used and I could find silk clothing in thrift shops. Now I might sew something from one of our new lightweight miracle fabrics to wear. I'm mostly van camping now.