The local big ASDA wasn't too bad around 9am when I visited. There was still fresh meat (though you'd need to be flexible as plenty was sold out but if you want meat you could get it), plenty of milk, bread and even paracetamol! No pasta that I could see (other than wholemeal spaghetti) and I forgot to look for rice. No toilet roll of course.
I figure by 1300 or 1400 there will be very little choice left at all as I got there only around an hour after opening (one member of staff told me that there had been a queue about 200m long at 8am when they opened) and stocks were dwindling but by no means gone.
As I think everyone sensible on this thread (god why can't more people be like the good people of RailUK eh?
) there's plenty of supply just to many people being ridiculous with what they want to buy.