Items that are essential are extra socks, because the trenches can get wet and muddy, leading to the fungus that causes trench foot. Once the illness is caught, medical help must be sought immediately, for if it is left go for too long, amputation of the foot may be necessary. But this can be avoided by the frequent changing of socks, leading to the need for extra pairs
U.S. World War I poster by N.Y. : American Lithographic Co is licensed under Public Domain.
Other important items include vaccines, for they help prevent diseases. Diseases are common due to the crowded living conditions inside the trenches. One cough and many others could be infected, for the trenches are wet and warm, perfect bacteria breeding grounds (InspirEd. Life in the Trenches. 2004).
Gas masks are crucial to survival, for they protect you from the poison gas spewed by the enemy. If your mask is not worn, you'll suffer for days until death.
Small Box Respirator by Larry D. Moore is published under Creative Commons Attribution-Share Alike 3.0 Unported
Bringing extra food is important, because many problems stem from hunger. Things like weakness and disease can be avoided in part by having plenty to eat. Although food is hard to come by, every bit counts.
Red Cross Parcel by Gaius Cornelius is published under public domain
Life in the Trenches. H Y Wheeler, 2004.