We were up in Sonoma County and a bit farther north to the Healdsburg area (compared to Napa) during the "crush" and and visited a couple of wineries. Many don't require reservations for visits/tastings but do for tours. A little research on an area will help, there are a lot of wonderful scenic wineries and tasting rooms throughout the area. It did seem like many spots are focused on the weekends for special dining experiences, etc., so Fri - Sunday may be better visit days and may have some added congestion. A reserved tour may not be a bad idea.
Yosemite may be an interesting experience during that time frame. There has been a lot of snow this year and it may not be done snowing yet. The peak flow of water - snow melt - in the rivers, streams and falls is typically about the Memorial Day time frame so visiting is very popular and the weekends especially are crowded. Here's the deal. Deals. Sometimes the flow is so intense that there is serious flooding and road closures and the valley can be extremely hard hit. Watch road conditions and reports, follow the NPS website info. The other deal is that the high country roads, the Tioga Road, Highway 120 which crosses the Sierra to Lee Vining gets over 9000 feet at Tioga Pass. The Glacier Point Road which reaches out to Glacier Point from the Wawona Road, is also fairly high altitude. These roads can't be opened until avalanche danger is past, and the plowing can take place safely, dealing with downed trees, rock slides, boulders in the roads, etc. Some high snow years, they may not open until after Memorial Day, although it's typically sooner as opposed to later. This year? Might be very late. If those roads aren't open, then all of the visitation is concentrated in and near the valley. So, it may well be very crowded or maybe even subject to closures. FWIW, by then, it's unlikely you will need chains even on the high country roads. But the travel info and weather sites will certainly have warnings and closure info as you get close to trip time.