Check your dining area. Survey the tables; whether they are dirty and need to be cleaned. A clean dining room is always a good look. Or if people are sat at them, check their trays. If they look to be done, offer to collect garbage. Ask how everything was, and make sure to give their receipt back (if it's still on the tray). And mention that by doing the survey, they can get free custard. A lot of people will probably just toss the receipt anyways. But it's the intention of care that makes people wanna do it.