Knights did not have combat packs over their body armor the way modern soldiers do. Their extra gear and daily supplies were supposed to be seen to by servants, carried on the extra horses/pack animals/wagons that were brought along with the army, and left in camp or in the baggage train during actual combat. Protecting the baggage train (and the lucrative possibilities of looting the enemy's baggage) was an important component of medieval warfare. In general, it seems as if soldiers of all varieties attempted to divest themselves of heavy equipment on the march if possible. While soldiers might carry their personal arms and march in armor (if in enemy territory or expecting ambush), they would often try to put as much of their heavy equipment in the baggage as possible. The French crossbowmen at Crecy famously suffered because their defensive shields were stuck in the baggage train and the French army was too congested for them to reach them quickly. Although I know less about Renaissance warfare than I would like, there is a large amount of art depicting mercenary soldiers in the period carrying their personal gear/supplies along with their weapons and armor. However, those soldiers are quite frequently wearing only a breastplate/helmet rather than a full harness. Armor became much cheaper over time, allowing the average soldier to be equipped fairly well for an affordable price, but a complete head-to-toe harness was still relatively expensive and comparatively rarer.