OOOOOOOOOOOOOOOOOOOooooooooooo........ that depends a lot on the mission, the time you are supposed to be in the field and a million different considerations. Gear taken may range from socks and underwear to change up to explosives, from a tin can opener up to a "boresight" or thermic sights.

Best way to find out is to find an army nearby and go and serve there for a while. You will learn in no time how those lists are made.
Remember that a way of thinking is more important than a gear list.