American soldiers mainly brought one of two rifles into the field. The model 1903 "Springfield" had won several international shooting competitions prior to the war and was renowned for its quickness and accuracy. To augment its slow production, American plants that had manufactured arms for the Allies began producing a modified version of a British rifle, known as the Model 1917 "Enfield." Both weapons utilized .30-caliber bullets, which were stored in a cartridge belt worn around the waist.

Although a haversack for storing provisions had been used by the American military prior to the Civil War, the Model 1910 marked the first time this carry-on was worn on the back instead of the side. Additionally, instead of having a bag-like body, this sack was essentially a strip of canvas that could be folded up and secured by straps. Another distinctive feature of this version was a detachable bottom section which could be shed to lighten the load. Although the Army continued tinkering with its design, the M-1910 remained in use until World War II.

Measuring approximately 2 feet long by a half-foot wide, the entrenching tool—or shovel—was fastened to the outside of the haversack. This apparatus typically received plenty of action, as much of the non-combat time in the trenches was devoted to trench maintenance, but it also had a use beyond the designed intention of digging.

"If you read the memoirs, one of the most effective weapons in close-quarter combat was the entrenchment tool," says Warren. "The entrenching tool gave a soldier leverage by being able to use two hands for strength while small enough to use in small spaces."

Besides the entrenchment tool, soldiers on both sides carried weapons that proved more effective in cramped spaces than the old-fashioned bayonet. The U.S. Army-issued trench knife had a triangular blade that could easily pierce clothing and leather, along with a spiked guard that doubled as a set of brass knuckles.

Another popular option was the trench club, which could simply be a police nightstick but was often designed with spikes or fitted with nails and other sharp objects to lend a medieval touch to the mayhem.

As the saying goes, "An army marches on its stomach," and to that end the mess kit provided a means to help tackle hunger. This kit consisted of a metal pan with a handle that folded over a lid/plate, while the accompanying fork, spoon and knife helped the user keep his fingers clean. According to Warren, American infantrymen were generally better-fed than their international comrades, occasionally receiving luxuries such as fruit and chocolate. They also stood out in one other regard, as theirs was the only army among the major belligerents that wasn’t regularly supplied with alcohol.

Along with subsisting on the meals delivered to the front lines, soldiers squirreled away emergency rations in their haversacks in case they were separated from their divisions. The typical American supply of "iron rations," so named because they were packed in tin cans, consisted of meat, bread and condiments such as salt and sugar. Many Allied soldiers also carried the notoriously firm hardtack biscuits, which normally needed to be soaked in water, crumbled and combined with meat to be rendered edible.

Given the danger of flying bullets and shrapnel, it was essential for a soldier to have a first-aid packet for either self-application or a nearby colleague to administer. Metal tins of about four inches by two inches typically carried gauze and a vial of iodine, which could be applied to the wound or dressing as a disinfectant. Unlike some of the other items, this case was usually kept in the front pocket of a soldier's tunic or another easily accessible location. Says Warren, "You don't want to be searching through your haversack if you're in sudden need of medical attention out there."

As indicated by the name, this government-issued booklet was primarily intended to help a soldier record payments received and owed. But it really served as an all-purpose log book, especially for similarly distributed items from other Allied countries; the British version, for example, noted information equipment skill and awards and provided space for its owner to write a will. Additionally, the paybook was commonly used to store letters from home, pictures, religious tokens and good-luck charms, and could be used to identify an unrecognizable fallen soldier.

Along with fostering a sense of civility, attention to personal hygiene helped ward off disease amid the unsanitary conditions of the trenches. Tucked away in the haversack was such personal-care items as foot powder, a bone toothbrush, tooth powder, and a soap bar and a dish. Doughboys also carried a shaving kit comprised of shaving powder and a Gillette safety razor, as opposed to the old-fashioned straight razor wielded by the British. And as it turned out, there was another important reason for keeping a clean-shaven face besides personal appearances.

Ever since the Germans unleashed the first chlorine gas attack in 1915, both sides continuously developed deadlier forms of chemical warfare and stronger equipment to endure these onslaughts. Crucial to the successful deployment of these masks was an airtight rubber face piece—hence, the importance of hairless cheeks and chin—which allowed the user to breathe without leakage. The typical American box-respirator model included a flexible hose that connected to a metal canister with purifying chemicals, as well as a nose spring and pad that kept the nostrils shut and forced breathing through the mouth. Soldiers kept this crucial mask in a knapsack worn around the neck and strapped to the chest.

With many long, idle hours between the action, soldiers could enjoy a diversion from their dreary environs by partaking in games. A deck of cards could easily fit into one's belongings, as could a small, foldable checkers set. Dice games were popular as well, with the British favoring one known as Crown and Anchor. Across the front, the Germans enjoyed a board game called "Mensch Aergere Dich Nicht" ("Man, Don't Get Annoyed With Me"), a precursor to the popular American board game Sorry.