Guess you never heard of foxholes? Usually OP or listening post position and other infantry unit's foxholes specs are wide/deep enough for 2+ men, not for just one---so they keep each other company and don't fall asleep in the same time, and having the enemy sneak up on them.
As for what other infantry men do in the real world(it means they are not there to protect/support the machine gun nest as their main/sole mission---it's the other way around), please read up on basic infantry squad/platoon tactics books that others already gave you. I'm sorry, I forgot you don't read stuff others gave you.....