Thermometer
First aid dental kit
Meds for digestive problems
Burn shield/burn gel
Supply of new "entertainment stuff" (crafts, board games,...)
Batteries, torch
Jump starter, if you have a car
Fresh herbs, salad greens, etc. if you have space for them
Very Lazy Garlic/Ginger/Chillies
Hankies
Travel bidet - can cut down toilet paper use
Period Products
Condoms, contraception
Shampoo, Conditioner, Facial Creams,...
Comfort food
Sewing supplies
If you have regular problems with thrush/BV/cystitis, it is possible to get some of the meds prescribed for future use.
I find freezing grated cheese and making my own pizza dough (+ passata/tomato paste/whatever I have around as pizza sauce) works out better in terms of how I use space. Napolina also make pre-made pizza bases that can be kept in the pantry and last a while.
If baking, find some good recipes that work with oil instead of butter (oil is easier to store)
Some cards for birthdays, weddings, funerals, christmas,... + stamps
If you have them, anything your pets may need. Pet stuff won't be top of the priority list in an emergency (or Brexit), so better to have more than less.
In the "nice to have but not really necessary gadget corner", I have found the sodastream and breakmaker really helpful. Plus, nothing tastes quite as good as freshly made bread with (tinned) soup. I also caved and got a table-top dishwasher. We don't really have space for a dishwasher but with three meals prepared at home, I simply couldn't keep up with the dishes anymore.