To the original poster, since you asked and probably do not know:
M= Mission, E= Enemy, T= Terrain & weather, T= Troops & fire sppt avail and -T= Time.
As Erick said, these ALL factor into your loadout. Besides, you may also be carrying unit gear, i.e.: litters, ladders, breaching equip., 60mm mortar rounds, and any other shoulder and back breaking gear in order to finish the job.