Definatly try to familiarise yourself with some of the different products, i’m thinking they will test your knowledge to see if you know the difference between the different types of coffee (Cappichino etc) (and no, i have no idea lol)
clean hands and nails, and hair would be important here, as would still being smart but not necessarily suited and booted a nice pair of trousers (or skirt) and a shirt with tie (or blouse) would be sufficient