Think Alice Waters/Wolfgang Puck movement of the 80s that supported (still supports) locally grown produce, cheese and meats.
Depending on the region of the vineyard of the CA wine, research the local vegetation, think of current climate and create a small plate. Do that with every vineyard.
Set out a cheese plate of CA cheeses: Cypress Grove, Humboldt Fog, Fiscallini, Point Reyes, etc...
If the tasting includes red wines avoid asparagus and artichokes. Reds typically do not show well when paired with these vegetables. Also, red sauces are best with Sangiovese, but Cabernet Sauvignon and other big, tannic red varietals don't show their best side with them. Keep them simple, perhaps crostini, breads with charcuterie, and the cheeses noted above. For Chardonnay, Viognier, Dungeness crab cakes (mini) would be lovely.
a nice spinach / baby green / herb salad with blue cheese or goat cheese and candied pecans (or walnuts) with a nice vinegrette is IMO very californian. i know you can get this type of salad thorughout the country now - but i always think its best when i'm home in ca. really b/c ca is the salad capital - any salad would be "californian."
also - some kind of toasted french bread spread with goat cheese and topped with roasted vegetables (and artichokes or olives or sundried tomato if your crowd likes that) is very californian. i like it with just the goat cheese and roasted veggies. so good.
I'm the original poster and should have clarified some things...
We actually live in Southern California, but often being so close to something makes the perspective more difficult. The ingredients shouldn't be a problem. However, we'd prefer to have everything be "finger food" and avoid needing two hands or utensils.
Great suggestions so far! Keep them coming.