Rich's idea of a picnic is perfect.  
In my book, there's no better location in the Valley for a picnic than Pride Mountain Vineyards, which is on the north end of Hwy 29 and straddles the line between Napa and Sonoma.  Tastings and picnic tables are on a reservation only basis, so be sure you plan accordingly.  Be sure to ask for a picnic table up the road (left of the parking lot) that overlooks Napa/Sonoma.  
First, go to Sunshine Foods, a great, old grocery in St. Helena.  It's a great destination to pick up sandwiches, salads, prepared foods, cheese, breads, dessert, bottled water, etc.  Other options include pricier Oakville Grocer, which Rich sited, or Dean & Deluca in St. Helena. 
With your reservation in hand, head up to Pride.  Take in a tasting and then move over to the picnic tables for your lunch.  (Editorial note: you'll likely spend 30 minutes or so being 'wowed' in the tasting, so be sure you bring your picnic wares inside.)  Note that Pride does not typically carry 1/2 bottles, so plan what you may want to drink (not drink!) with your picnic lunch.  The vineyard is known for their Cabernet [2002 released this fall], Cab Franc, Merlot, and also have a very nice Viognier.
Sunshine Foods 
1115 Main St. (between Spring and Pope Streets)
St Helena  - 707.963.7070 
Pride Mountain Vineyards 
4026 Spring Mountain Rd. 
St. Helena - 707.963.4949 
www.pridewines.com As far as other recommendations, here are a few notes on restaurants and vineyards that we visited last summer, most of which are in Napa. If you have any specific questions, just let me know ... 
Restaurants: 
Bistro Jeanty 
6510 Washington St. - Yountville 
707.944.0103 
www.bistrojeanty.com Recommendations: tomato soup with puff-pastry, haricots verts salad, terrine de lapin, lamb tongue; steak frites; mussels; cassoulet 
Martini House 
1245 Spring St. (at Oak) - St. Helena 
707.963.2233 
www.kuleto.com/Martini.htm Recommendations: great outdoor space to enjoy a nice lunch. Good items include the ahi tuna tartare, goat cheese salad, torchon of foie gras, chicken pot pie 
Terra 
1345 Railroad Avenue - St. Helena 
707.963.8931 
www.terrarestaurant.com Recommendations: hamachi and salmon tartare, black code with shrimp dumplings, grilled lamb t-bones, dulce de leche crepes 
French Laundry	
6640 Washington St. - Yountville 
707.944.2380 
www.frenchlaundry.com Notes: What else can you say except good luck in securing a reservation, which are available two months to the day. 
Vineyards: 
Cakebread Cellars 
8300 St.Helena Hwy 
Rutherford - 800.588.0298 
Notes: Provides a relaxed, informative and enjoyable visit. Has two tasting options, $5 and $10, which provide the opportunity to taste various wines. Fun, successful vineyard with great options for everyone; known for their Chardonnay, but also have a good Sauvignon Blanc, Rubiat, Pinot Noir; good wine club, too. 
Joseph Phelps Vineyards 
200 Taplin Road 
St Helena - 800.707.5789 or 707.963.2745 
www.jpvwines.com Notes: Beautiful vineyard with beautiful wines. Tastings of approx. five wines for $10/head, with a supplemental charge of $20/head for a tasting of their trademark Insignia. One of the high-end vineyards in the Valley; tasting provides good sampling of various offerings; need to split the Insignia jus to try how great it is! 
Robert Sinskey Vineyards 
6320 Silverado Trail 
Napa - 800.869.2030 or 707.944.9090 
www.robertsinskey.com Notes: Strength is in its Pinots. Tasting room is open late so it can be one of your last stops on a given day. 
Schramsberg 
1400 Schramsberg Road - Calistoga 
North on HWY 29; though St. Helena; Left on Peterson Dr.; right on Schramsberg Road) 
707.942.2414 
www.schramsberg.com Notes: Great tour; one of the best sparkling wine vineyards in the Valley 
Caymus Vineyards 
8700 Conn Creek Road - Rutherford 
707.963.4204 
www.caymus.com	Notes: Pretentious vineyard that bottles a fantastic Cab. Don't bother asking about their Conundrum offering as it's not a focus. Reservations are a must, and you can't be late as they literally shut the door on late-comers. 
Gary Farrell 
10701 Westside Road - Healdsburg 
707.473.2900 
www.garyfarrell.com Notes: One of our only stops in Sonoma. Known for their high-quality Pinots. Reservations required for tasting and tour 
Groth Vineyards & Winery 
750 Oakville Crossing - Oakville 
707.944.0290 
www.grothwines.com Notes: Good Cabs, Chardonnay and Sav Blanc