Excel. Honestly, there really is no other software to do the job for you. As long as you know how to create the formulas, keep track of your inventory and make the time to make a list of your inventory, you should have no problem with Excel.
My restaurant recently switched to toast pos, and I am just now starting to get the inventory and costing input. It is very intuitive and simple to use, and obviously will be able to aid me in inventory tracking.
Excel is always a great back up system if you have nothing else to go on.
As mentioned above, learn and use Excel or a clone. once you figure out the formulas you need, it is pretty easy. the only thing easier would be if your place found an inventory control package as part of a POS system, a whole lot more expensive than a copy of Microsoft Office.