Soldiers carried masks, bags, maps etc. when they entered the battleground. Things they carried could save their lives, also, these things represented their responsibilities.

Soldiers are not cold-hearted people, some of them even did not want to kill. However, they did not have choices, they wanted to protect things they wanted to protect, it could be their countries, their families, their lovers. Soldiers also had emotion but emotion would show their weakness to enemies. So, they chose to hide their sentiment, became the same replicas as killing machines for things they wanted to protect.