If you go to the shops to buy items that are essential eg vegetables, fruit, milk, bread, then there has never been anything stopping anyone picking up some crisps, chocolate biscuits, or a pair of sock s at the same time.
I believe that the intention of the government is that people aren't going out to the shops all the time, but only when they need to replenish essential supplies. A further issue is that what might be essential to person A may not be viewed the same way by persons B, C and D.