Just think, as far as original meaning of the word “haversack” is concerned, this soldier’s carryall might just as properly have been called a “gunny sack.”
That is, the original German term was haber sack, literally “sack for oats,” and it referred especially to the bag, usually of canvas, in which a cavalryman carried oats for his mount.
French and English cavalry adopted both bag and name, with slight alteration, and, naturally, found the bags convenient for holding personal items in moving from place to place.
And so did other travelers, the flexible haversack, with strap over the shoulder, being easier to carry than is the modern suitcase, though perhaps less commodious.