How do I make a meal deal with a burger, fries and a drink for one price?

Use a bundle. Open Marketing → Bundles, press Add bundle, give it the name the customer will see, set the bundle size to three and the price. Choose the items they may pick from, for example any burger, any fries and any drink. Save with Active on. A bundle is a price, not a discount: the three items are re-priced to the deal, so the receipt, the minimum order and VAT all see the deal price. You can decide whether the bundle earns loyalty stamps. The Promotions & marketing tab in the docs has the guide.