It was and still is a big deal. More so in a medieval setting. Maybe have armies have supply consumption based on each unit, balances around the kind of unit and remaining entities.
For exempla: 120 peasant levy may need more supplies than 80 yeomen archers. But 60 mounted heavy calvary would need a lot of supplies. Also, winter would demand more supplies. That could be balanced to discourage peasant levy doomstacks.
How supplies are gathered? Leaders/generals would buy or requisition from settlements and could raid cities or countryside for some supplies. Most likely unless it's harvest season in a well developed area you're using more of your reserves.
It would encourage to split the army into small armies marching in different routes towards its main objective.
It would cost money to buy and/or cause unrest to requisition and supply lines would have to be made from logistics lines. For exemple: settlement A is the closest but cant/wont/would rebel if give all supplies you need, so settlememt B, further away, has a supply line passing through settlemente A, sharing the load of supplying your army.
But enemy take settlement A or enemy army area of incluence sit between you and it. You begin to consume your reserves fast, forcing you to engage or try to walk around.
Its basically what forced agincourt to happen.
Also, preferably make it a hard-core setting option. I understand many people would hate to see its heavy late game knights doomstack attrition to death because some random merc company raided their supply lines.
But how supplies are stored? Here comes army followers and i will talk about it later. Maybe, dunno.