The wedding is in Temecula wine country. There are several wineries along Rancho California Rd that would be great for wine tasting on the weekend. We've heard Doffo is great for reds, and Akash has both beer and wine. Apparently, there is also a "secret" underground barrel room at Ponte if you want to explore. If you like sweet treats, try Wilson Creek's Almond Champagne and ask about their chocolate shot glass experience.
There are several golf courses in the area. Two of Nick's favorite's are Journey @ Pechanga and Temecula Creek Inn. They are both within 15 minutes or so. There are also others in the area, so look around to see if something piques your interest.
If you're feeling lucky, Pechanga is a big casino nearby. It's about a 20 minute drive.
The wedding is in Temecula which is quite a bit inland by about an hour. If you'd like to see the beach, we recommend staying in downtown San Diego when you fly in, or staying in to La Jolla, Del Mar, Pacific Beach, Encinitas, or Oceanside - and then commuting to the wedding.
If you're looking for night life, Old Town Temecula is near a 15 minute drive or so from the venue, and there are several bars there.