Sonoma /Napa have several fun activities. We have listed a few below that you can look into.
1. Wine tasting
You can book wine tasting tours from several vendors such as Wine Country Journeys, Terrific Tours, and Platypus Tours (and many more you can find on Yelp) or you can drive yourself around -- just share tastings and stop drinking when you need.
We personally love the following wineries. VML, DeLoach, Russian River Vineyards, Seghesio Family Vineyards, Marry Edwards, Iron Horse, Jigar, Joseph Jewell and Porter Creek.
If you want a laid back and younger audience for your wineries, you can visit
Harvest Moon Estate & Winery, Balletto, Hook & Ladder, Sunce
2. Calistoga Hot Springs
Calistoga, CA has some beautiful hot springs and spas you can visit.
3. Bike tours
You can rent bikes from almost any city and ride around the vineyard roads.
4. Russian River Kayaking and Rafting
There are several rental companies you can find for this.
5. Hot Air Balloon Tours
There are several rental companies you can find for this.
6. River Rock Casino
I assume this is small, but could be fun
7. Safari West (Animal park)
8. Old Faithful Geyser of California
9. The Ranch at Lake Sonoma (horseback riding)