If the customer brought some items to the counter, then went back to get more, or if the cafe diners had ordered entrees, but were still to order the mains, you may want to Park the order.
To do so, simply add the products to the sales cart. You can add a name to the sale, but it is not necessary.
Click on the Park button at the bottom of the Sales Cart. The sale will automatically go to Sales History, and you can continue serving the next customer.
When the customer is ready to pay, you can retrieve the sale from Sales History, as detailed in this article Complete a Hike sale from Parked orders