I see from your other topics you are considering a food tour and a ghost walk.
Look at the other offerings from London Walks Company. They have many history walks (Roman London is a fav) and neighborhood walks (old neighborhoods that date back to medieval period or the Victorian era) that are all interesting. Go to www.walks.com to see if there are other walks that might be of interest to you.
They have a couple of Harry Potter Walks and a couple of Beatles Walks that are very good.
About the food tour you say you might take in your other topic you posted....you don't need it. The 2026 version of RS Best of London tour, the group goes on a food tour of the East End. Then another day, at lunchtime, they take you to Borough Market, where you can do your own food tour by wandering among the many food stalls and sampling different dishes. Free samples are also handed out at the cheese stands. So I would not add another food tour....just my opinion.
Your topic here is "Best of London Regrets (?)" so I will say, my only regret was not spending more time in museums. The tour goes to the British Museum one afternoon, but a couple of hours would not be enough for me. I would return to the British Museum on one of your days off, as there is enough in there to keep a person entertained for 3 to 4 days.
Two things I would add, that are not included in the tour's activities......
The Victoria And Albert Museum--the V&A.
Day trip to Hampton Court Palace--short trip easily done.