The run of thinking is that a No Deal Brexit (and the attendant supply chain carnage) will not be allowed to happen, but when it comes to food and medical supplies, safe is definitely better than sorry.
I reckon Mrs May's painfully aware that the minute the shops run out or the power goes off, her government is over. And, somewhere, Edward Heath would appreciate the irony.
I also imagine that as a diabetic, she's already got her own medication supplies arranged in the event of import delays.
Personally, I haven't started stockpiling anything as my needs are quite basic, but from an exporting point of view, as my biggest customers for ConsoleMAD are in the EU, particularly Scandinavia, I'm debating whether to pause overseas ordering until I can be sure there'll be no delays.