I like the idea of a food cart, but just imagine how bothersome exploring would be. Your exploring warriors would either have to turn around halfway, or you'd have to send a food cart to them if you don't want them to starve to death. I think smaller stacks or individual units should be able to supply themselves when on fertile land. So for example if they're standing on a tile that has a yield of 2 food, then it can supply for 2 soldiers. Food carts would still be implemented of course. It would also make tundra and desert warfare more interesting. Actually, why not make the food cart into a transport cart? In warfare you can use them to carry food to the troops, and in peace time you could let it send materials (hammers) to growing towns, and food to growing towns.
Perhaps scouts and explorers could have special property that they would not need the food chart, but all other units would ?