Whenever I get too lazy to do laundry and run out of clean pillowcases, I would use old shirts as pillowcases. Hence I thought of actually converting an old shirt that's about to be thrown or used as rag anyway into a pillowcase. Here's what I did:
1. Take the measurements: get the appropriate length and width of your pillow to be transferred to the old shirt.
2. Cut the sides to create a basic rectangle form (you'd have to cut most of the sleeves and the collar).
3. Sew the cut sides together and the seams ('pillowcase opening') if necessary.
4. Here's your new 'shirt pillowcase'! :