We live overseas so brexit shouldn't affect us in terms of supplies etc.
However we do always keep a small supply of things here, and tbh its been used at least twice each year.
As an idea:
1)Recently there was flooding higher in the mountains, in term it somehow contaminated our drinking water supply (the entire area not just our house). We couldnt drink from the tap without boiling the water first for 11days. The shops had plenty to replenish, but it was helpful the first few days that we had a small amount of drinking water at home without having to rush out. like I said you could drink once boiled, so we didnt need to buy all our water as boiled for cooking and hot drinks.
2)snowfall. Supermarkets were open fine, main roads clear, but our small lane wasn't and couldnt get the car out for 3 days. Meant we could have walked 1km to shops, but would have been a pain carrying more than a small bag home.
3)dh and I both had the flu back in February. neither of us would have been safe walking or driving to the shops for at least a few days as both dizzy, fainty and similar. again had enough soups in freezer, some part baked bread and medicine to just ride it out.
So yes, In our recent experiences, easy food for 3-5 days that you might want to eat when ill or its cold. plus a few days water is a good minimum amount to keep
Top supplies used here:
Part bake bread - lasts a few months and we just use up and rotate
Oat milk - keep in cupboard, easy for porridge. makes nice hotchocolate
salted prezel, stick type things - good when ill. easy snacks
mulled wine - tastes even better when your stuck! and drink enough you wont mind