"Up Alabamians!", a painting by Don Troiani, depicts General Bee addressing officers and men of the "Huntsville Guards", 4th Alabama Regt. Enlisted men are wearing back packs labeled "H G". This would not have been uncommon for Alabama companies on the field at Manassas.

The Alabama Volunteer Corps was established by the state legislature on Feb 24, 1860. The "Huntsville Guards" did not belong, but many other Alabama companies on the field at Manassas were AVC members. In some cases donations from the community (usually a city or large town) paid for AVC uniforms and equipment. Arms were purchased by the State of Alabama or acquired from the U S armory at Mount Vernon AL. The state quartermaster also contracted for knapsacks, canteens tents and other field equipment which were issued to volunteer companies accepted in service of the State of Alabama.

Of course the question covers volunteers from other Southern states. Volunteer companies from other states probably followed similar conventions.