If you're thinking about the place itself:
* Home: This is the most common opposite, meaning you're eating at your own residence.
* Street food vendor: This refers to food sold on the street, rather than in a sit-down establishment.
* Takeout/Delivery: This means getting food prepared elsewhere but not dining in.
If you're thinking about the experience:
* Informal/casual: This contrasts with the formality and structured nature of a restaurant.
* Spontaneous: This suggests eating somewhere unplanned, as opposed to a planned restaurant visit.
If you're thinking about the service:
* Self-service: This refers to places where you prepare and serve your own food.
* Catering: This implies food being brought to you, rather than you going to a restaurant.
Ultimately, the best antonym for "restaurant" depends on the specific situation and what you're trying to express.