Below is a 5 item guide to tell you what you need to have the best chance at surviving the trenches
Army Heritage Museum B.A.R. by U.S. Army licensed under public domain
Nothing will be more useful than your handy dandy rifle during trench warfare. You'll need it in case anyone comes over the top at you or you have to go over the top. This will protect you from enemies, near or far.
Lots Of Extra Socks
BLW Pair of socks by David Jackson licensed under Creative Commons Attribution-Share Alike 2.0 UK: England & Wales
These extra pairs of socks will assist you in many ways. For one, you will have some extra socks to change into when yours get wet. Also you can wear two or three pairs at a time to prevent wetness. This will help protect from trench foot and gen green.
Feldspaten by Mediatus licensed under Creative Commons Attribution-Share Alike 3.0 Unported
This is the building block for trench warfare. The entrenching tool is basically a miniature shovel. It helps soldiers dig their trenches that they will shelter in. This tool will help keep you safe from the natural elements.
US WWI Gas mask with bag by historicair is licensed under Creative Commons Attribution-Share Alike 3.0 Unported Explanation
As the war evolves, a gas mask will be essential to staying alive during the war. The function of this tool is pretty obvious, to protect you from breathing in harmful gasses. This tool will protect you against any gaseous enemy attacks.
WWI Medical Kit by Thomas Quine is licensed under Creative Commons Attribution 2.0 Generic
The final thing on this list that you will need to survive the trenches of WWI is an emergency medical kit. This way, if you or a buddy get injured on the battlefield, you can have a temporary fix for a major injury or a complete fix for a minor one. This kit is essential to your overall health during the war.
That is the last of my 5 items
If you abide by this list right here, you have a chance at surviving the trenches of the raging WWI, just don't get your hopes up
Apocalypse WWI: Episode 3. Apocalypse: World War I. CC&C, n.d. Web. 23 Mar. 2017.