I've just been to Sainsbury's. In central London, on my way home from work (for possibly the last time for a few weeks). Let me tell you what I saw:
There's not any dried pasta on the shelves, or tins of beans/tomatoes. Difficult to get raw chicken or bread flour.
There are loads of fresh fruit, vegetables, bread, biscuits, crisps, packets of ham, coleslaw, salads, sandwiches, drinks, sweets, milk, cheese and yogurts. (Actually when I was there the security guards were chortling amongst themselves about the run on tins and the fact that nobody was buying any bananas or carrots.)
Don't stress. Eat normally. Plan as if you were going to do your big shop stretched a bit further out, but don't worry. Buy a couple of butternut squashes, those things last months!
I have to admit that my DH is very worried about stocking up on pasta, but I keep telling him "between the spaghetti, fusilli and the lasagna we have three bags of it. And we haven't even eaten it once in the last seven days."