I was a child during WWII and fabric wasn't readily available but my grandmother would save her feed sacs for me to have a dress. As you grew, it took three or four so it was thrilling to get enough to make a dress. Flour came in them later. Also, sugar came in sacs that were a course off white and had writing on them. Your sacs look exactly like I remember feed sacs. They were sewm together on the side and the selvage was across the top.