Everybody else here captured the uncertainty in the world, but even without specifics you can still do a tabletop exercise without jumping all the way into a rabbit hole and see what you’d need to have to spend three days without being able to buy supplies. Most of those kind of lists just end up being things you’d need anyway: water, food, any prescriptions, some local currency if credit card machines are down, etc. Decide how much you think some event is likely and how much budget you have and react accordingly, or don’t. Take it as an opportunity to change out the batteries in any smoke dectectors or battery powered radios, maybe top off any power bricks you have for charging phones.

If you decide to stock up on something there are a lot of resources out there already on what makes sense. If you decide not to stock up on anything then be aware that people might not be willing to share if something does happen; you had the same opportunity to prep and the same information that everyone else did.

Most of my knowledge of UK preparedness is either from WWII documentaries or dubious sources: https://www.youtube.com/watch?v=kgwaOEg0Uqo