Although wineries and restaurants are open year-round, expect some rain December through March. Most restaurants require two weeks' to one month's notice for a weekend night. Consider lunch in lieu of dinner at a high-end restaurant. You can sample the same food for less money and can often get a table just a few days ahead. Leave your name on a waiting list.
Most places confirm reservations the night before and fill cancellations from their list.
Call around 5 PM to check on day-of dropouts. The grape crush in September and October is an exciting time to visit, when vineyards are busy with picking, squeezing, and tasting. Ask your innkeeper or hotel concierge to call on your behalf. They often know someone at the restaurant and can pull strings. Just show up.