To understand how ill served Medieval armies were in terms of logistics, consider what the Romans did and how they did it. The Romans were supremely organized in all they did. Literacy was encouraged, and in the Roman armies nearly half their troops may have been capable of reading and writing. This was important because about five percent of a Roman army consisted of technicians, clerks, and supply specialists. These troops received extra pay and/or exemption from manual labor so they could keep track of what supplies the army had on hand, how long these would last, and where new supplies were coming from. A Roman army kept records, lots of records. There were lists for everything, including how much of each soldiers' pay (and Roman troops were generally paid on time) was to be deducted for food, clothing, weapons, and burial expenses, not to mention the annual party. When any of these items were needed, the Roman army clerks had it available. The Romans built a network of roads (some still in use) throughout their empire to speed the movement of troops and supplies. All cities and many towns had military purchasing agents who received reports from the army detailing how much food, shoes (hob nailed sandals), weapons, and other supplies and were they were to be delivered. The army commanders had finance officers who arranged for suppliers to be paid promptly, thus encouraging timely and accurate fulfillment of military contracts.
The Romans knew how much food (by weight and cost) their troops would consume each day. Their army clerks kept daily records of how many troops were with each unit. Army purchasing agents kept track of what supplies were available in their area, and how much of it was for sale and for how much. Paper reports were carried up and down the Roman roads to keep everyone informed of who needed what and when. The Romans usually managed to control the sea lanes also, and would rent, buy or build the shipping they needed for each campaign.