My wife and I are planning on trip to SF/Wine Country for this October, and given that she doesn't drink much wine, are looking for some activities other than visiting wineries. We're staying in Yountville Tuesday - Friday, and have a full slate of dining already planned, including reservations @ The French Laundry. But we need a few things to do between lunch and dinner .

Here's what I have on my list so far:

1) Round Pond olive oil tour
2) visit some of the small towns in Napa/Sonoma: St. Helena, Healdsburg, Calistoga, and Sonoma all seem like they'd be worth checking out just to walk around, shop, etc even if we didn't go to any wineries.
3) take a hike, maybe at Bothe-Napa Valley SP or Jack London SHP? Are there other/better (short) hikes around?
4) hot air ballon ride has come up, but we're spending all our money on food. Is it really worthwhile?
5) gourmet food markets: Sunshine Market, Oxbow Public Market. Other food markets?

Any other things it would be fun to add to the mix? I'm not trying to plan a specific itinerary and I'd prefer things we don't need to reserve in advance.

Spa treatments or a mud bath treatment in Calistoga.
Safari West

With that many days, you could also head over to Bodega Bay/Jenner/Armstrong Redwoods.

Lucky you!! The French Laundry!!

Sonoma has some interesting historic buildings and it is fun to hang out in the Healdsburg's lovely town square and have lunch there.

We are going to Napa in 2 weeks. Someone suggested touring Cowgirl Creamery, if cheese interests you. Also Culinary Institute of America at Greystone has interesting things to do and see. We are going to French Laundry too!!!!! I am SOOOOO excited!

Bike ride thru the vineyards?
Bar hop up Washington St in Yountville?

This is incredibly gorgeous country, looking in various parts like Tuscany or the South Downs in England. Just riding the backroads could be a great vacation, especially if you take a day to go over to the coast as MichelleY suggests. Point Reyes looks like the Highlands of Scotland. Take the Oakville Grade Road from the Napa Valley into Sonoma. Definitely go to Jack London State Park. Eat at Taylor's Automatic Refresher in St Helena as an antidote to the French Laundy. Go antiquing. And on and on.

If you like art, you can't go wrong with the di Rosa Collection. It is an amazing private collection:
http://www.dirosaart.org/

We took a cooking class at Greystone that we really enjoyed.

We also loved the hot air balloon ride, but it may be cold at sunrise in October.

You have received good advice. Cooking classes at Greystone are a great option. So is visiting the di Rosa Preserve - probably the most interesting non-wine destination in Napa County and one of the most interesting art collections I have seen anywhere.

Since you are coming in October, maybe the new ziplines will be in operation in Yountville:

http://www.napavalleyziplines.com/

Or take a segway tour:

http://www.segwaynapa.com/

Balloon rides can be really cold in the early morning hours in October - bring your ski jackets.

Usually, the weather is fantastic in October - great hiking weather. Bothe and Jack London are both fine but the best ones are on the coast at that time of year.

There have been a lot of questions about other things to do in both Napa and Sonoma on other forums, just wanted to say that the 101 Things To Do Guide is available 'on line' as well as in hard copy when you get to CA. Very helpful with things like locations for good hikes, museums/ galleries that are lesser known, just about any type of activity level is addressed, too.
Its actually produced for numerous travel destinations throughout the country.

Even though you are not into wine tasting, a visit to the Francis Ford Coppola winery in Geyserville would be interesting. It's actually more of a museum than a winery - lots of movie memorabilia, a mint condition Tucker auto, and an upscale restaurant. It is situated on beautiful grounds including a pool and spa. Geyserville is one of the more fun little towns, with a wild west meets wine country feel to it.

zootsie: >> Even though you are not into wine tasting . . .

Jack London SHP is more interesting than Bothe-Napa in that it includes visits to the house Charmian built that contains memorabilia from their south Pacific voyage, has the ruins of the Wolf House, and also some buildings from the farm that Jack London wanted to develop as a model farm.