I saw mention of haversack in my history book. What does that word mean?

Throughout the history of conflicts on home turf and beyond, soldiers suiting up for battle relied on their haversacks to keep their supplies handy. Slung over the shoulder, the bag with the long strap served as a big purse for military personnel.

The haversack's size and construction allowed soldiers to pack in rations, utensils, and personal belongings. Doing battle with such a clunky carryall, however, wasn't easy. (Imagine charging the enemy with a fully loaded bookbag swinging at one side of your body.)

Although cumbersome, haversacks continued as a mainstay in military outfitting from the Civil War through the early part of World War II. A wardrobe change, brought on by need for a more manageable way to tote around battle gear, introduced the backpack.

From Chapter 1 of The Red Badge of Courage, by Stephen Crane:

Others spoke of tattered and eternally hungry men who fired despondent powders."They'll charge through hell's fire an' brimstone t' git a holt on a haversack, an' sech stomachs ain't a'lastin' long," he was told.