0 to suddenly buy as much food, fuel, etc. as you can because you are worried about something bad that may happen and that may mean that there is not enough food, etc. available:
1 something bought suddenly, especially because you are worried about something bad that may happen and that may mean that there is not enough food, etc. available:
They think: "I'm not going to panic buy but I'll have to get extra supplies because everyone else will panic buy".
They are all clamouring for turkey. So out I go to panic-buy one and freeze it.
Mention the store to many men and the name conjures images of last-minute panic buys on Christmas Eve.