When looking at your add-ons and extras it is important to choose a featured item. A featured item will always be displayed at the top of your list. They will also always display prominently with an image and a description. On the non-features items, you would need to click on them to see this information. If you only have a few extras, they can all be featured.
It is best to choose something that's a good-selling item here for you. Something like a bottle of Prosecco or similar. Choose something simple that will maximise your sales opportunities.