A picnic does not need a park. Sometimes it is nicer on the floor, close to the speaker, with plates balanced on a magazine and cold glasses sweating onto the rug.
Keep the food hand-friendly
Think fritters, toast, fruit, torn cheese, and one thing that can sit happily at room temperature.
A little mess is fine. A lot of cutlery is where the mood starts to leave the room.
Make the setup feel deliberate
Use the linen, open something chilled, and put the good bowl in the middle even if lunch came together in ten minutes.
The point is not effort. It is making an ordinary patch of afternoon feel like a place to stay.