Are advance tickets necessary in London during winter holiday period

I was in London last holiday season from 15th through the 22nd. It was a bit of a last minute trip, so I started looking a month in advance and here are the tickets that were sold out or I had to buy on resale market.

• Kew Gardens Christmas: https://www.kew.org/about-us/press-media/christmas-at-kew-2019. This was one of the highlights of the trip. Kew Gardens at night with the lights and music is spectacular. I did not get the tickets in time and had to buy them off Gumtree. I don't know if they are still available, but if they are, you need to book now.
• Pantomime at the Palladium: https://www.palladiumpantomime.com/. Waited too long and it was sold out. They are completely sold out (just checked except for 2:30 show. Note, I could not find these on the secondary market.

Here were the tickets that I wish I planned better for, but I could get in:

• Hamilton. I waited until two night before as they were sold out for the nights I wanted to go, but a few nights before they started to open up a few seat and I score Orchestra Center 7th row for 200 pounds each. It was well worth it. You can always try the Lottery. The give away a limited number for 10 pounds each ticket (max 2). I won the lottery in San Francisco (took me months), but 2nd row Orchestra center, so you never know.
• Westminster had very limited opening time due to Christmas-related services. I couldn't get advanced tickets so came early in the morning (no problem), booked the verger tour and the Queen's gallery, but had limited time due to a closure at noon. We also attended one of the evensong Christmas services. It is free, but line up at least 45 minutes before opening for a good seat.
• Gingerbread City: https://www.thegingerbreadcity.com/. Last year it was the V&A and I didn't know about it until got into town. Had to buy tickets for our last day in town due to lack of availability. It is at the Somerset House this year. It was one of the highlights of our visit. I love architecture and sweets.

No problem getting in:

• Churchill War Room
• Winter Wonderland: https://www.timeout.com/london/things-to-do/winter-wonderland-guide. No problem getting in, but we met some folks in line at the Westminster who told us go before 7:00 as they waited about 45 minutes to get in. We went at 6:00 and no crowds, when we left at 9:00 it was wall-to-wall people.

Restaurants: it depends. if there is a place you really want to go to, i would book reservations. We tried to get into a couple of restaurants and they were just completely booked. I wanted to go to Rovi for our anniversary dinner and we did get in, but we sat at the bar (actually loved it). If you are not wedded to a particular place, there are plenty of great food options in London.

I’ll only speak to those sights I’ve visited during the late November to mid-December timeframe (Tower of London, Westminster Abbey, the Eye, Hampton Court palace, Windsor Castle) over the past 4 years. We didn’t wait longer than 10 minutes to get into any of them. Only once did we make a dinner reservation. If there is a particular restaurant you’d like to dine at, and it’s popular, I’d opt for making a reservation.

What is it that makes the panto a must see? I'm intrigued but I wonder if it's something that might escape me. Does it help to be a local to be into it? Also, to confirm, they're only done at Christmas time, but they're not christmas themed at all, right? I really only have time for the theater one night during our trip and I had planned on seeing a more "serious" play or Shakespeare but maybe I should reconsider.... just trying to figure out best way for a memorable trip (and I'm sure whatever option I go with will be fun, but I like to gather opinions :))

Panto is slapstick comedy. There are elements that are crucial to the theme and that is a man in drag and excessive vocal audience participation. It's a centuries old tradition, often considered uniquely British but actually has its roots in Italian street theatre.

Personally I'm too much of a grump to enjoy them and I find Victorian era theatre seats too uncomfortable for a man of my height so I avoid theatre and pantomimes entirely however I do think it's a unique experience if you've never been to one. It's fun, no-one takes themselves seriously and it's typically an enjoyable show. If, however, you are looking for a serious play then forget panto.

it helps to understand some of the inside jokes which often have a different meaning - both funny or ironic - to the children and the adults. Often the adult joke is risque or a bit rude - in a good way.

There is often at least one celebrity among the cast who often has lines in line with their persona.

There's 3 phrases to know that are crucial when watching a pantomime, "he's behind you, oh no it isn't and oh yes it is".

This is a theoretical comment not based on experience, because I do not travel to Europe in the winter.

December is a relatively wet month in London. On average it gets over 2 inches of rain, spread over about 10 days. I wouldn't want to have to stand around outside unnecessarily. Of course, having pre-purchased a ticket is no guarantee of totally avoiding lines if there's a back-up at the security check or something like that, and it doesn't sound as if you're too likely to run into really long lines. But getting wet at that time of year, when the temperature could be in the lower 40s(F) or even the 30s(F) in the early morning or evening, wouldn't be much fun.

Kew at Christmas is totally amazing, but sold out weeks ago