In WW1 gas mask where needed to protect from the deadly gasses so it is a tool needed to have in the trenches if the enemy ever throws gas in the trenches so that you can breath and get out.
Most trench soilders lacked the amount of food to keep a human healthy. Many of the men would go days without food because the rats would steal it from them while they tried to sleep. Most of the food that they would get lacked nutrition and was never even hot. So bring your own food that will last for a while.
Many of the men in the trenches would have to stand in the mud for hours causing many foot diseases. To not get trench foot which was one of the most common things in the trenches they would have to change their socks daily. But the military was low on socks so many of the men would have to get their feet cut off because the trench foot got that bad. So bring pairs of socks so that you wont have to worry about trench foot.
In the trenches a shovel was more important than a rifle. it helps them find cover when needed and helped the soilders dig farther and deeper trenches if they needed. So if you want to survive you need to bring a shovel because it will help you a lot.
Make sure to bring the proper clothes because if you don't and its winter you'll freeze to death. if its hot out you'll need a different pair of clothes because you might have a heat stroke and we don't have much clean water in the trenches. If you want to survive bring the right type of clothes.