The "Steward's Kit" on the left was carried into battle by the steward himself or another soldier who accompanied the assistant surgeon on the field or at the forward dressing station. It contained supplies for bandaging wounds, splinting fractures, administering stimulants or anodynes (painkillers) and other emergency treatments.

The Regimental Hospital .........from the "Civil War Medicine Website"

      Although Charles Johnson wrote this many years after the war, it is one of the best of the comparatively few accounts of military field hospitals. Johnson had enlisted as a boy of eighteen, and was assigned to hospital duty in the West; he was with Grant in the siege of Vicksburg and later took part in the expedition into the Bayou Teche country. His account goes far to explain the failure of medical services in the war and to place responsibility not on the medical officers but on the state of medical science at the time.

        In the field the Regimental Hospital department was allowed two small tents for the officers, medicines, etc.; another small tent for the kitchen department and supplies, and a larger one for the sick. This last, known as the hospital tent, was about fourteen feet square and was capable of containing eight cots with as many patients.
        In the field we almost never had sheets and white pillow cases, but made use of army blankets that were made of the coarsest, roughest fiber imaginable. In warm weather the walls of the tent were raised, which made it much more pleasant for the occupants.
        However, the policy that obtained was to send those who were not likely to recover quickly to the base hospitals, though this was not always to the patient's best interests, for these larger hospitals were oftentimes centers of infection of one kind or another, especially of hospital gangrene, which seldom attacked the wounded in the field.
        During a campaign our stock of medicines was necessarily limited to standard remedies, among which could be named opium, morphine, Dover's powder, quinine, rhubarb, Rochelle salts, castor oil, sugar of lead, tannin, sulphate of copper, sulphate of zinc, camphor, tincture of opium, tincture of iron, tincture opii, camphorate, syrup of squills, simple syrup, alcohol, whiskey, brandy, port wine, sherry wine, etc. Upon going into camp, where we were likely to remain a few days, these articles were unpacked and put On temporary shelves made from box-lids; and, on the other . hand, when marching orders came, the medicines were again packed in boxes, the bottles protected from breaking by old papers, etc.
        Practically all the medicines were administered in powder form or in the liquid state. Tablets had not yet come into use, and pills were very far from being as plentiful as they are today. The result was that most powders- were stirred in water and swallowed. In the case of such medicine as quinine, Dover's powder, tannin, etc., the dose, thus prepared, was a bitter one. The bromides, sulfonal, trional and similar soporifices and sedatives, had not come in use, and asafetida, valerian and opium and its derivatives were about all the Civil War surgeon had to relieve nervousness and induce sleep.
        Among the surgical supplies were chloroform, ether, brandy, aromatic spirits of ammonia, bandages, adhesive plaster, needles, silk thread for ligatures, etc. There were, also, amputating cases well supplied with catlins, artery forceps, bone forceps, scalpels, scissors, bullet probes, a tourniquet, etc. But while all the instruments were washed in water and wiped dry to keep from rusting, such an idea as making them aseptic never entered the head of the most advanced surgeon.
        There was an emergency case, about the size of a soldier's knapsack, and, indeed, intended to be carried on an attendant's back like a knapsack. In this emergency case were bandages, adhesive plaster, needles, artery forceps, scalpels, spirits of ammonia, brandy, chloroform, ether, etc. This emergency case, or hospital knapsack, was always taken with the regiment when the firing-line was about to be approached, and where the First Assistant Surgeon was in charge and was ready to render first aid to any who might be wounded.
        This first aid, however, never went further than staunching bleeding vessels and applying temporary dressings. Thus attended to, the wounded were taken to an ambulance, and in this conveyed to the field hospital in the rear, generally out of musket range, but almost never beyond the reach of shells and cannon balls.
        Arrived at the larger field hospital the patient was cared for by the surgeons and male nurses. The wounds were examined and dressed, but never antiseptically, for no one knew the importance of antisepsis or how to put it in practice; consequently, every wound suppurated, and so-called laudable pus was welcomed by those in charge as an indication that the patient had reached one of the mile-posts that had to be passed on his road to recovery. Careful hand washing and nail scrubbing was never practiced before operations or in dressing recent wounds. And yet, for the most part, the wounds in the end healed satisfactorily. The fact that those receiving them were, in the great majority of cases, vigorous young men had much to do with the good results. Here it may be proper to say that in the Civil War by far the largest proportion of wounds were made with bullets from what were called minie balls. These were fired, in most instances, from single-shooters and muzzle-loaders, such as the Springfield rifled musket, the Enfield rifled musket, the Austrian rifled musket, etc. These bullets weighed an ounce or more, and the guns from which they were fired would kill a man nearly a mile away, and that they produced large, ugly wounds goes without saying.
        When a minie ball struck a bone it almost never failed to fracture and shatter the contiguous bony structure, and it was rarely that only a round perforation, the size of the bullet, resulted. When a joint was the part the bullet struck, the results were especially serious in Civil War days. Of course, the same was true of wounds of the abdomen and head, though to a much greater degree. Indeed, recovery from wounds of the abdomen and brain almost never occurred. One of the prime objects of the Civil War surgeon was to remove the missile, and, in doing this, he practically never failed to infect the part with his dirty hands and instrument.
        When Captain William M. Colby of my company was brought from the firing-line to our Division Hospital he was in a comatose state from a bullet that had penetrated his brain through the upper portion of the occipital bone. The first thing our surgeon did was to run his index finger its full length into the wound; and this without even ordinary washing. Next he introduced a dirty bullet probe. The patient died a day or two later.... These facts arc narrated to show the frightful handicap Civil War surgery was under from a lack of knowledge of asepsis and antisepsis; and it is needless to say that no reflection is intended to be made on our surgeon, for he was making use of the very best lights of his day, dangerous as some of these were....
        I think wounds from bullets were five times as frequent as those from all other sources. Shell wounds were next in frequency, and then came those from grape and canister. I never saw a wound from a bayonet thrust, and but one made by a sword in the hands of an enemy. In another chapter a reference is made to a man who received a deep wound in the upper part of his thigh, which, after some days, proved fatal. Not long after the wound was received the parts began to assume a greenish tinge and this became of a deeper hue, and when after death the parts were cut down upon, a copper tap from an exploding Shell was found to be the ugly missile which had inflicted the injury that, in the end, proved fatal.
        Where so many men are grouped together accidents of greater or less gravity are liable to occur. On the whole, however, our regiment was fortunate. We lost two or three by drowning and one by a steamboat explosion .... and I can recall but three who received accidental bullet wounds. One of these was a pistol shot of small caliber . . . , and the other was from one of the Springfield guns that was supposed not to be loaded. Looking back, I can but regard our record in this direction as especially fortunate, when the handling of so many loaded guns through so long a period is taken into account.
        The only light vehicle in the regiment was our hospital ambulance, a four-wheeled vehicle with bed on springs and covered with strong ducking. The rear end-gate opened with hinges at its lower part for the convenience of putting in and taking out very sick or severely injured patients. The driver of our hospital ambulance was a soldier by the name of Throgmorton, who knew his business, and attended to it. He was an expert horseman, and kept the pair of bays under his care well-groomed and properly attended to in every way. They were, to a degree, spirited, and when the occasion called for it, were good steppers. Besides serving its purpose in conveying sick and wounded, our ambulance proved useful as a sort of family carriage, upon several occasions taking certain of us well ones "here-and-yon."
        For service about the hospital men were detailed from the regiment to serve in the several capacities of nurses, cooks, and ambulance drivers, etc. Service of this kind was known as. "special duty," and not a few came to have duties. Especially was this true of the men who no little aptness in their new cared for the sick, some of whom developed quite a little insight into disease, and were frequently able to make tolerable diagnoses and prognoses.

-JOHNSON, Muskets and Medicine