Was doing some research and ran across this, for folks visiting Napa mid-week. Tues/Thurs there's an all-day shopping tour and cooking class centered around Oxbow Market. Not cheap, but could be a lot of fun as a break from endless drives from winery to winery, especially if you've got visitors from out of state who've done Napa before and are looking for something different to do:
Oxbow Market Tour and Cooking Class
Description: "Step off the beaten path and join Julie for an insider's tour of the Napa Valley culinary scene and learn the delicious secrets of Napa. Start the morning at the market with Julie, browsing the produce market with its sparkling fresh produce from local farmers, and selecting cheeses and salumi from specialty vendors. Oxbow Public market offers the season's finest and freshest products. Learn how to select and cook the unique vegetables and fruits found only at boutique markets. Next we visit a winery for a private tasting to select wine for our meal. Then, on to the kitchen, for a hands-on cooking class where we will turn our bounty into a wonderful wine country feast. Lunch is served on a beautiful outdoor patio or in an elegant dining room."