As the advice is not heeded by some shoppers I firmly believe it's time a limit on items bought at supermarkets should be introduced now eg only allow one of each item bought eg fish (one packet); chicken (one packet of breast, one thighs, one wings, etc), oil (one bottle), etc, so that others will not go without. It might be tough on large families, but unprecedented times require unprecedented measures; a few more trips is better than empty shelves.
The availability of basic foodstuffs is essential and important at times like these for reassurance and encouragement that food supply is forthcoming and not disrupted.