At some point you will want to maintain a larger army even have a negative output to have a army larger that you can hold.

1- Granary

Granary are essential to keep your extra food, specially when you plunder a lot those extra grain must go somewhere.

2- Satellite city  

Satellite cities are a great way to store you extra troop near you city specially those 9 and 15 food field. Store your troop there while your maxing your granary and get them back with you have to attack or defend your self.

3- County, state capital or Luo Yang

If you have a county, state capital or a member of your league has one, it can be a good place to store your unit and food, since they have a large food output and a lot of food storage space.

Plus your help your league by defending it.

4- Hide troop in other city

At some point in the game, those small city around you won’t be plundered at all, since you know their food output you can put that exact amount of troop in it.

For your information, Starting village usually have : 12 of food /hr (18/hr if you kill there starting hero)

5- Rank

Your rank increase your granary storage capacity, so do a lot of duel and scrimmage to get the items for the court quest.

Other tips for managing food from the koram forum

The Art of war – How to build a large army and support it.

How to build a main city on a 15 food field.

By the way, keep your gift voucher to upgrade high level ressource field (specialy if your shu or wu)