Your grocery costs could be categorized as Inventory, and your supplies would be listed under Supplies.
Under Common Expenses (if you listed your business as Catering) you will see a place to enter food purchases (produce, baking ingredients, etc.) and also your Catering supplies (disposable trays, flatware, dishware, napkins, runners, etc.).
For Inventory, if you purchase your groceries on an as-needed basis, you won't actually have a beginning and ending inventory, so you can enter zero in both places on that screen. Then on the screen Let's get the costs of your goods you would enter the amount of your purchases for the year.
[Edit 01/18/18 9:34 AM]
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.