Every July and August San Luis Obsipo hosts a Mozart Festival. We aren't the dress-up kind of music family, but we did enjoy the Music in the Vines. We went 5 years ago for the first time and again this last trip.
The Music in the Vines is located at the Marin-Wyerick Winery in Paso Robles. They have a grassy ampitheater where you bring a blanket or chairs to enjoy the music. Of course, you can't bring in your own wine as they sell their own there. You get a free glass too!
I wish I would have remembered but you can bring your own picnic dinner.
What better way to enjoy the evening but being outside, under a starry night, sipping wine, and listening to fine music?