Well, I have a different perspective from my background in healthcare, as I can understand what the preppers are thinking about. I would like to say first that I am not one of those hoarders, but still feels the need to stock up if the virus situation gets worse.
Toilet Paper - I can see alot of people making jokes about stocking toilet paper. It function does not only include wiping off downstairs. But it can also wipe off sweats, tears, saliva, sputum, organic or non organic spillages, which can become crucial in infection control at home. Just say, you have an elderly mother, or a young child who is sick with corona virus, and are sweating and coughing. The best way to rid of those secretion / sweat / sputum or vomit is via toilet paper, and discard. You cannot flush facial tissues or wet wipes down, and the process of retaining them before discarding creates a chain of infection risk.
Stocking up in general - People stock up, for many reasons. For example if you have a loved one who is immune compromised, then it is only sensible to stock up in case there is localized transmission of the virus. And of course, one would never know if suddenly you are ordered to self isolate. Take for example this article...
https://www.theage.com.au/national/coronavirus-closes-epping-boys-high-school-20200305-p547dn.html
Because of one boy, the entire school was ordered to self isolate over the weekend as the public health official working on contact tracing. Now, what if one of your family happen to be one of the close contact? Then the next step would be for testing, and self quarantine for 14 days. Now, if you dont have any backup, what are you going to do? Break quarantine? Get uber eats? Order coles online? yeah, may be you can do it now, but what happens when the virus spread, and the delivery workers gets sick? Call the police? As far as I can see, the pandemic plan does not include methods on how to deliver food and supplies to the isolated, only how to dob in and lock up those who appear sick into modified stadiums.
N.B. Please please do not kill the messenger, I am merely thinking of other people's perspective which I usually do on this forum.