Trip to London Nov. 21 -Dec. 4

To Windsor there is no point in buying tickets ahead of time, the fare is no different, and there are no seat reservations.
But assuming you don't have a National Railcard, the cheapest way is to use contactless payment, the same as you would on the tube and buses, if not using a travelcard.
The only difference is that Windsor is not included in the daily/weekly cap.

Doing that (on the day or contact less) also allows you to use the Windsor Riverside route from Waterloo, if the Paddington route is up the creek on the day for some reason.

Contactless is £15.80 return off peak (any time weekends, after 0930 weekdays).
Interestingly any time return (out before 0930) is cheaper with tickets at £19 return, compared to £20.30 on contactless.

Sounds like a very nice trip. To answer your questions:

-You should be fine with the clothes you are describing. This time of year it tends to rain a lot so it's more about staying dry than staying warm (tho it will also be chilly).
-No need to book trains in advance to Windsor or Eton- you can even just use contactless payment and tap/in out on the day.
-Unless it's a very popular pub, you don't need to make bookings for lunch during the week. On the weekend, especially Sunday, I would book to be safe. For dinner, I would normally book to be safe, especially towards the weekend. You don't normally need to book for trivia night tho I would check the website to see what they recommend.

By the way, the Frida Kahlo exhibition is pretty good but just be aware that a lot of it (probably more than half) is artwork from people who were influenced by Frida. I was a little disappointed in how little original Frida there was- just to manage your expectations.

Good luck with your planning.

Thanks Stuart and Cat VH. Your replies are very helpful. That is disappointing about the Frida Kahlo exhibit. I had hoped it would have had just her work.

The evening temperature in November can dip below freezing (or it may not) but for Kew I’d suggest being ready for temperatures just below freezing possibly with a bit of rain thrown in

You are welcome! One other thing I forgot to mention- since you are planning to visit the National Gallery, you may be interested in their current Renoir exhibit: https://www.nationalgallery.org.uk/exhibitions/renoir-and-love

That's one I would recommend booking in advance.

Thanks, Bill. I am thinking packing a thermal top and bottom and wool socks might be a good idea for when we are going to be out and about on the chillier days.

Thanks, Cat VH for the info on the Renoir exhibit. I will add that to my list.

A couple of other things I have on my list for our similar trip before Christmas are the Agatha Christie exhibit at the British Library and the Peggy Guggenheim exhibit at the Royal Academy. And also the Museum of London opens its new location Nov 28.

Thanks, Laurie Ann. Yes, I would like to add the London Museum. We went to the previous one years ago and enjoyed it. Where it is just opening though, I wonder how mobbed it will be. I am not sure if we will be able to fit it in on this trip.

Thanks, Cat, for mentioning the Renoir Exhibit. I had noticed that somewhere, but forgot to put it on my list.

We will be in London Nov. 27-Dec 3, then head to Chester and Bath/Wells until the 13th.

Whereas overnight a great review (in a TR) of the Frida Kahlo exhibition has been posted on Trip Advisor, showing that everyone has different approaches and views to such things.

That's a slight misinterpretation of what I said about the Frida Kahlo exhibition. I did not give it a bad review but shared the fact that about half of the works are from other artists, to help people know ahead of time what to expect.

Thanks, Cat and Stuart for the clarification/additional info on the Frida Kahlo exhibit. I was going to skip it but as it is just across the bridge from our lodging we will head over to see the exhibit anyway.

I notice that the Ampersand Hotel is near South Kensington, so I would recommend a visit to the Natural History Museum (free entry) to see the Dinosaur exhibits there. Best to avoid the crowds of kids at weekends, if you can.

Dippy - the replica Diplodicus skeleton - billed as the 'World's Favourite Dinosaur' that used to be in the entrance hall of the NHM is now on a tour of the UK (yes, really) but there is now a female Diplodicus called 'Fern' (and, no, I don't know how you can tell male dinosaur skeletons from female ones) made of bronze in the garden below the museum's entrance. She is surrounded by ferns in the garden and the whole thing is nicely done and quite photogenic in my view. Worth seeing if you are nearby, especially for a dinosaur nut.

Mary- I spent last Christmas (Dec 23-29) in London. The lights at Kew are amazing. I wore a pair of cashmere long underwear - purchased at the Uniqulo in London. My Cuddle Duds took up too much room in my suitcase, so they were left behind. Someone on the forum recommended cashmere long underwear. They are very light and warm. Layers are key. I also took a pair of waterproof Oboze sneakers.

Christmas in London was my favorite time. You're in for a treat. London will be bursting at the seams, but brilliant.
Happy Travels!

Thanks, BillS719. Thanks for the heads up about the dinosaur being on tour. I have informed my husband of that fact so there won’t be a meltdown from disappointment on the day we visit. LOL! He can geek out on the one outside. Are the animatronic ones still at the museum? I’ll have to check. Maybe those were just temporary. Thankfully we have been to the Museum of Natural History before and saw the dinosaur then. We plan to combine a visit to that museum and the V&A with the Jurassic Tea. I will do that on a weekday.

Thanks, Stacie. The thermals don’t take up much room so we will bring them. And we have waterproof footwear. We were in London during the Christmas season 25 years ago. I agree it is really special at that time. I can’t wait.

I was just remembering this as I posted it in another thread the other day- but if you are going to the Natural History Museum I cannot recommend highly enough seeing the Wildlife Photography of the Year exhibition: https://www.nhm.ac.uk/visit/exhibitions/wildlife-photographer-of-the-year.html

We go every year and it's always great. I know it's not dinosaur related, but you may both enjoy it anyway :)

Oh my gosh, thank you Cat for letting us know about the wildlife photography exhibit at the Natural History Museum. We have seen videos about this competition in the past and the photography is amazing. My husband and I are photographers and will definitely be getting tickets for this. Edited to add - tickets are booked. We are both so excited to see this exhibit! Plus Cheddar Man who is my husband’s distant ancestor!