There is a small Spanish supermarket open on a Sunday on the road directly behind the Paseo (promenade) in Sabinillas from the roundabout go towards beach turn left at the bottom and about 150 meters along in the Estepona direction
The Halal butcher near to the tyre place and Ferreteria Morales (close to the Sabinillas roundabout) is open on a Sunday.
Going up the hill to Manilva Pascal y hijos on the first sharp bend is open on a Sunday.
Some of the small local shops in Manilva village are open on a Sunday morning including one that sells meat.
And don't forget the garages stock a range of basics.