It would depend on what you use. Do you cook from scratch a lot? (You may find yourself doing that here, to save money.) If so, think of the things you use regularly. If you post them here, we can tell you if we've seen them.
From my kitchen:
Beef marinades, like Claudes. I have found A-1 sauce in Tesco from time to time, but no Claudes or mesquite smoke liquid. Hickory liquid smoke is readily available in my area.
Any of the seasoned salts (other than garlic). We have missed Lawry's Seasoned Salt (until we brought some back from a trip recently). Mrs. Dash is a "go to" of mine and ,while I can order it online here, it's rediculously expensive to do so.
Pumpkin Pie Spice. (Yes, you can mix your own, but it's a PITA.)
Dill pickling spice. ("Pickle" here is not the same as "pickles" in the USA.) Other supplies for pickling, if you do your own. Including jars and lids.
Really good quality black peppercorns, such as Telicherry. (I've found some online, buth they were overpriced for the quality.)
Mexican oregano. (Italian oregano is available, but Mexican is difficult to source.)
Good quality cumin. (Again, there is cumin available, but it's not got the "punch".)
We have found fantastic smoked paprika out of Spain, but not sure how supplies will be once Brexit hits. Fortunately, it stays fresh for a long time if kept in a sealed tin.
Huey Fong chili and garlic sauce is very hard to find here. If you are into that. (Secret Santa sent me some, tho!
) Good "dipping" salsa is as scarce as hens teeth. The "local" stuff is kind of like spiced ketchup.
Herbal teas are limited. Hard to find Stash Teas and we haven't seen Zhennas on the shelf anywhere. If you have a particular favorite, you might want to bring some over with you to hold you over until you find more.
Flavored coffees (aka vanilla hazelnut, chocolate rasberry, etc.) are pretty much non-existant, as are mild-roast coffees. (The coffee served "out" in Glasgow would take paint off the car it's so strong and bitter!) We haven't found anywhere other than the Christmas market to buy whole flavored coffee beans, and then they are dark roasted so we have to cut the grounds with a non-flavored coffee. Actually, I can't remember finding anywhere to buy even regular light-roasted (or any roast) whole unflavored coffee beans. Sigh. Hawaiian coffee beans are just a dream to be remembered.... So we flew home with two pounds of coffee beans literally on each of us - in the pockets of our coats! And more in our luggage. USA TSA was perplexed, but let us through.)
True vanilla extract. What you find on the shelves here is either diluted with water or has sugar added. It's more a vanilla flavoring than an extract. It's ~Very~ hard to find a good vanilla extract here. I've had some problems finding almond and mint extracts. (Same problem, when finally located - they have additives and are not true extracts.)
Ceylon cinnamon. There are other varieties available, but it's hard to find Ceylon cinnamon.
Sometimes you can find these items online, but they will be exponentially more expensive than in the States. I use a US company called Vitacost.com and occasionally they sent me a "% off" coupon that pretty much obliterates the shipping cost, if I spend $100 with them. I buy from their organic lines (usually Frontier Co-Op), in bulk, then. So right now I have plenty of Mexican seasonings, cinnamon, and pumpkin pie spice. I also buy a lot of Bob's Red Mill from them, when they have sales. You can get a lot of Bob's products here now, but it's still cheaper, on sale, to have it shipped over. Particularly almond flour and cashews. (Cashews are like gold here!) I also like a UK company called BuyWholeFoodsOnline.co.uk that has been very good - the quality is there, although you can't always find what you need with them.
Again, take a look at your spice rack and tell us what is there - we can give you some indication as to it being available here.
