The answer to this question is very wide! "Grain and grass" refers to the food eaten by soldiers, including forage and bean crops eaten by war horses (including staple food and non-staple food mentioned today). If there is no water source in the station, supply drinking water! The general's personal preference for food and drink. It also includes the supply of weapons, armor, gunpowder and oil during military operations! Trench transportation and so on! To put it bluntly, it is today's logistics! Some of these materials were shipped from the rear! Some troops are supplied by places where they pass during the March! Then there is "trying to plunder"! Individuals are also allowed to carry appropriate rations according to the nature of the battle! Most of this work is the responsibility of the army and local grain and grass officials! When a large corps is fighting, there are often grain and grass bases not far from the front line. Most Mongolian legions bring their own food when they fight! When a large group fights, flocks of cattle and sheep follow! There is also a kind of beef jerky made by special technology, which is very small and will swell when soaked in water! A basketball is big enough 10 for many people to eat 10 for many days! It explains why the Mongolian legion was able to dominate Eurasia at that time.