This is one of my favorite parks in Los Angeles and they do wine tastings with Silverlake Wines throughout the summer. There are food trucks, or you can bring a picnic, sit in a pretty park, listen to some tunes, and drink some wine.
Tickets are $35 for the wine tasting or $50 is you want to do the wine tasting and tour Frank Lloyd Wright's Hollyhock house.
Parking can get intense, so if you can I would recommend public transit or carpooling, otherwise plan on getting there early in the evening. Purchase tickets and find more details here http://barnsdall.org/events/wine-tastings/