Unique must-buy items in London or England in general?

My sister will send me right back if I don't get a coronation tea tin for her this spring.

Carol, it sounds like TWO trips to England for you this year! ; )

Tea Tins, Tea Towels, Walkers Short Bread cookies, key chains such as: Elizabeth’s Tower, a crown, a black cab, or a bobbie hat. Heritage Biscuit Tins. Wallace and Gromit water bottle. Harry Potter deck of cards.

EDIT:
I’m old school and use an Oyster Card.

My favorite card holder is from the British Library and depicts Alice in Wonderland and the Mad Hatter. Think I got it in 2015.

Have another holder from the British Library which is The Bloomsbury Group.

I'm a little spoiled since it's extremely easy to get British goods here. Walkers Shortbread is everywhere and we have a local British grocery store, plus a World Market. A cheese shop where I can get Stilton or Shropshire blue cheese but sadly they haven't had Sparkenhoe Red Leicester for a long time. The hardest thing to get here is British candy because of product licensing and such so it's candy that I bring back and usually not for myself. Last trip I probably brought back nearly 30 pound of candy that was for my coworkers. For myself it was a box of black licorice fudge from Borough Market. I have some friends in the UK now and theyve promised to bring me some coltfoot rock candy.

VAP, I LOVE black licorice - the strong intense flavor ones! What licorice or other candy do they like? : )

Oh boy! When it comes to black licorice I'm rather selfish, so I have a oh so secret stash of Icelandic chocolate covered black licorice toffee that's very dear. But I do keep a candy jar on my desk at work and one of the candies that makes a rotation is Katjes Salty Fish Licorice.

But it's been a tradition for each trip to shower lots of candy on the coworkers with my goal that it's usual sort of stuff you'd find in a market or grocery store. What would I find in a Albert Heijn in Amsterdam or Tesco or Sainsburys in London, but not available here at home. So lots of various Yorkies, Wispa, Flake, Dairy Milk and other Cadbury made by Cadbury (since Hershey makes Cadbury in the US). Might have brought back a few jars of blackcurrant jam too.

But it's hard to share the black licorice, especially fudge. That was selfishly savored.

Remember that Museums and Art Galleries in the UK usually have amazing gift shops to buy all kinds of goodies in!
Marks and Spencer's Food Halls always have great things to bring back, as do shops like Boots and SuperDrug for different beauty and cosmetic type things.

Those lovely garden shops.....I hear your pain.... ;)

+1 for museum gift shops, and they are great for books that may not be on the shelves here. Museum of London was a great source for some titles. They had John Stows 1598 Survey of London last year.

Tea towels! Over 3 trips I have probably amassed over 30 of them; my favorite is Warhol's depiction of Queen Elizabeth, have that one in 2 colors. They are a daily happy reminder of visits to a beloved country.

Always fabric and a small craft kit from Liberty, and I usually find chocolates there or at Harrod's.

I am a sucker for the titles published by the British Library (mysteries & women writers in particular) and bring home as many as possible. Last trip was tough as I also went to Bath to visit my favorite bookshop, Persephone Books--at least 20 lbs of books came home with me!

Best souvenir, and free, to boot: a feather from one of the Tower ravens. I only got lucky once though I keep an eye out every time.

Well, at a church rummage sale I scored an original, small (7 in) English china plate, commemorating the June 2, 1953 coronation of Queen Elizabeth II. As I remember, I paid £5. It was especially meaningful to me since as a very small lad, I actually attended the coronation with my late mother.
Via our black-and-white TV, of course.
Good luck finding one of those QEII plates! Something from the coronation of King Charles III would no doubt be easier to find this year, but likely much more pricey.
I also brought home one of those double-decker red London Transport buses. This was about 3 inches long, not an original, but easy to pack.

When I go to museums, cathedrals or other places that have gift shops I usually buy leather books that has the name of where I’m getting it.

Always grab some Crisp for a friend in different flavours (prawn is one of her favourites). The British store sells them here but they are crazy expensive I think it was $4 at Christmas for a small package, For myself I like to check out Marks and Spensers. They have a Salt and Vinger chip in the shape of a french fry that I loved as a child when we use to have the stores in Canada.

crista, I’m always a sucker for Liberty of London fabric, too. I buy it over here, but the price pains me considerably. It’s pricey over there, too, but much less so. I always buy fabric in every country I go to. Last year I brought back some fabric from a store in Berlin that I just converted into a baby quilt for my niece.

In line with the candy theme, I love the rhubarb custard hard candies - boiled sweets? I always bring home a hefty bag of these along with some proper Cadbury items and different biscuits from the shops (Custard Creams make me so happy).

I like to bring home nativity sets from places I've traveled and have purchased from F&M, York Minster and St. Paul's Cathedral. Putting them out at Christmas makes me smile and remember each shopping trip.

At the Covent Garden Market, I picked up a set of plaster stones that hold tea lights with pebbles set on a saucer of sorts - not entirely sure how to best describe it but boy do I love it and every day it takes me back to that trip.

I agree with tea towels form gift shops at attractions you visit. They are useful, easy to transport, and not usually readily available at home for the places you might buy them when you visit. Plus they instantly say/show from where they were obtained.

I am still using the Harrods tote bag I bought in 1986.

I buy Christmas ornaments wherever I travel - I have two different Harrods bears and hopefully I'll find something like that this year and will also plan to get something coronation related.

This will probably sound extremely silly, but one thing I always buy are marshmallows, preferably from Tesco's or similar stores. Just the store brand. My first visit to London, my friend and I were for some reason amazed that the white and pink ones tasted differently - since most of the time the US ones with different colors don't have different flavors. They melt better in hot chocolate too and are so soft. I did find out that the Haribo brand ones aren't the same - my brother was in Scotland and I told him about the pink and white marshmallows and he mailed me a bag. I didn't have the heart to tell him that the Haribo ones are the same as in the US, same flavor and consistency.

I also used to buy ibuprofen gel since it was prescription only in the US but I think that's changed now. I also used to get a bunch of Lush items but I hardly use them any more so I might get some soaps but that's it.

Paracetamol.

Their linen tea towels are wonderful. Different teas in lovely tins for tea drinking friends. Sturdy cloth totes from Harrods or even Whole Foods-you know the ones that advertise location, not so much the store.

I think you will find amazing gifts there.

In addition to looking in all those wonderful museum gift shops, I also quickly checkout the home and houseware sections of home and even hardware stores. I’ve found some unique teabag holders and once bought a toast rack. I’m not sure about the sugar aisle in the UK but I like to check out the different shapes and sizes of rock crystal sugar in Germany to fill my sugar server. I never use sugar in drinks myself but I like a pair of tongs, the zucher container and beautiful sugar crystals to offer guests. Doesn’t hurt to have a beautiful tray and a tea towel too. The V&A had some beautiful ones last summer.

If you know anyone who is a fan of football (soccer) bringing them a team scarf would probably go over well.

I couldn't get my partner to leave the gift shop at the V&A I think they are now solvent thanks to her.

Keep in mind it's 2023 and we live in a world economy, it isn't that hard to get anything delivered to you from anywhere in the world. As noted, Cost Plus and World Markets often have sections of British goodies and many cities have British themed stores, tea rooms, restaurants.

Maybe a bit of a different answer, but I like to take reusable grocery bags when I go shopping to places like Target and Publix.
I love to find them over there as they are generally well made and interesting designs. My favourites are from Waitrose and whenever I shop here in the US I get a lot of compliments on them.
For a normal “must have” for me is half a suitcase full of sweets😋.