I wouldn't expect anyone visiting Napa to cook their own food -- after all, this is home to The Culinary Institute of America, The French Laundry, and other world-class and Michelin-rated restaurants.
However, if you happen to like cooking your own meals and you like seafood (and you live here or have a vacation home or an extended stay with access to a kitchen), then there's a little place you might want to check out called Osprey Seafood Market.
This is a basic seafood shop, nothing fancy -- it's a small, no-frills building tucked off of Solano Rd (which runs parallel on the west side of Rt. 29 on the northern part of Napa). But they have a reasonable selection of seafood that you might not be able to find at one of the local grocery stores.
I was in the mood for cooking some seafood on the way home from work today, and I was originally thinking fish -- maybe a Moroccan-style monkfish with tiger prawns. But then I thought about lobster, which I haven't had in a while, and one minute later the Napa VINE 10S drove past Osprey, with a sign out for Maine lobster, $12/lb.
They did, in fact, have monkfish (not cheap at $18.95/lb, though) but I went with a live lobster ($15), took it home and steamed it in saltwater, served up with lemon butter (melted butter with juice of one lemon freshly squeezed into it) and a side of Trader Joe's "Polenta Provencale", spicy creamy polenta with spinach and peas. I couldn't decide on which wine to pair with it, but decided to base it off the polenta dish flavor rather than the lobster, so I went with the Ochoa 2003 Chardonnay I bought at his tasting room in Calistoga recently. This one has a bit of apple, some sweet flavor like toffee, and a little muskiness. There's oak there, but it's weird because I don't taste it but can definitely smell it. It turned out to be a good pairing.