By Luz28 (Own work) [CC0], via Wikimedia Commons
The gas mask was used to protect soldiers from breathing in the chemicals that would cause severe damage or kill them slowly. They then used rags and googles later on but that didn't work. Then they finally developed an actual way to protect themselves against gas.
Shovels were used to dig trenches as cover. They would be safer underground than be in an open field even the trench would collapse but the at wouldn't happen till artillery targeted them.. The shovel was said to be more important than a gun.
The machine gun is a very deadly weapon during this war because it can mow down a line a troops fast. These guns killed 90% of soldiers so stay covered. They would shoot at soldiers that were unlucky enough to poke their head out.
By Joshua R. Murray (english wikipedia) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
These helmets were used as defense against shrapnel. Bullets would bounce off this light metal helmet. The helmet would save many lives of soldiers that would actually where it.
The bayonet was used for close quarter combat. When trenches had enemy soldiers infiltrating it then they would fight using their bayonets. They would keep them from range of enemy distance of a few feet.
"Commons:Contributing Your Own Work." Wikimedia Commons, commons.wikimedia.org/wiki/Commons:Contributing_your_own_work. Accessed 12 Feb. 2017.
"Commons:GNU Free Documentation License." Wikimedia Commons,commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License. Accessed24 Sept. 2013.