Question about scheduling wine tastings in Napa - do you need a reservation everywhere?
Last time we were in Napa (5 or so years ago) most places did not seem to require reservations, but it appears that most of the wineries we are interested in do require reservations now. We will make reservations at the places that are "must visits" for us, but if we end up with some extra time or drive by someplace that looks interesting, can we get in without a reservation? Are there wineries that don't require reservations? We are going in mid-November, so it should be a less-busy time, if that makes a difference.
At many places you need a reservation. Some of the larger wineries along highway 29 or Silverado Trail you do not need a reservation to taste. For tours you need a reservation typically. Places off the two main highways you will most likely need a reservation.
Most smaller places have use permits that only allow them to be "open by appointment." You won't see them advertising an open tasting room, as a result, but just make yourself a list of phone numbers for spur of the moment tastings--call around, many will be able to accommodate you with an immediate "appointment." Use your judgment--highly allocated cult wines that sell out won't give you a tasting if it isn't close to the release and they don't have any wine left to sell.
I did most of my tasting in Sonoma last trip, but there were plenty interesting places with no appointment necessary. Most of them charged $10/tasting, deductible from purchase. My new favorite thing is to spend time at one winery, and after bonding a bit with the person pouring, ask where else nearby I should try, given my taste.
I think your strategy is a good one, that's what I did the last time I was in Napa -- made a few reservations, and marked other places that I was interested in on the map so that if we had time, we could stop by. Keeping the numbers of those places handy so you can call them is a good idea too, though many places will let you drop in if they're not too busy. Pick up the free Napa Winery (or something like that) magazine that's at all of the wineries and hotels at your first stop -- it has some really useful maps, and great lists of wineries, their phone numbers, and whether they require reservations or not. Super useful freebie.
Most of my favorites require a reservation. That said, Plumpjack is just 'drop in' and a nice visit. As other posters have said, some of the major brands on the major strips are as well.
Some wineries just really require a "head's up". eg, if it is Saturday at 2pm, and you realize you'll want to stop by somewhere at 3pm, you can call them to see if they can accomodate you, and sometimes they'll say "yes"