If you're running low on stocks with your products and don't want customers to be able to order these products if they're out of stock then follow the steps below to make it disappear as one of the options when add-ons are out of stock. 

Managing inventory

When adding a product or editing a product scroll down to the very bottom where you see the "Tax, Inventory & More Section", click on it. Now select Yes on the "Manage Stock" and new options will appear called "Stock Status" - this will send a warning message of low stock and "Quantity -  place a numerical value on how many you have on stocks then hit "Save" at the top right.