And actually this would be interesting to chart - does this actually correlate to your kitchen usage? Ideally there should be no wastage in ingredients, but what happens if you find out that each day you're selling 10 muffins but using 20 eggs?
I think an ideal-ish system would be either to integrate to the POS system or have some kind of iPad/tablet app so you can tap in orders as they come. Just needs to be a basic counter that tracks how much is sold throughout the day. If you have POS data, then you can be even more canny and see finer resolution data (e.g. early lunch vs late lunch).