Since I don't know the details on your sales process I am not sure if this applies. Our method is to count buns, sides containers and beverages (bottled water and soda cans) before/after the event. We pre-fill 6 oz stryo containers with 4 oz of sides (hot & cold) so this works for us. At the end of the event we calculate up how many of each we sold and compare that to our gross sales.
Do I smell SMOKE?????