We go through hundreds of takeaway boxes and bags. Can I track packaging as well as food?

Yes. Add boxes and bags as ingredients on Menu → Ingredients & suppliers, counted in pieces, with the price you pay per piece and the supplier you buy them from. Then add one box to the recipe of each dish that goes out in one, on Menu → Recipes & food cost. Every sale takes a box off the shelf, the box's cost sits inside the dish's food cost, and a par level tells you when to reorder before you run out on a Friday night. F&B inventory here is anything you buy and count, not only what goes on the plate.