Some good advice upthread. I agree there is no point prepping for food stuff you can buy in shops, that just adds to the general panic buying issue. But definitely think (calmly!
) about how you would prep for all the shops apart from supermarkets and chemists closing, as I think that is what is next and some people haven't though enough about that.
So for example before it becomes too unsafe to go out and postal deliveries stop altogether, I am trying to accumulate:
New board games our family is already into board games so picking up a few fresh ones has been a great thing.
Colouring books and felt tips for me, for mindfulness and also as a way of dealing with crushing boredom.
Seeds and compost as others have said, growing some stuff is going to the next thing people think of and lots of folk are already buying gardening things and seeds in their droves and they are getting harder to find, especially salad leaves seeds etc.
Non food household essentials Like laundry liquid, washing up liquid, drain cleaner, and perhaps more towels so you can ensure everyone in the household always has their own towel at all times.
Music I have two musical instruments which I have neglected learning to play, now could be the perfect time. Is there something you've always wanted to learn to do?
Books - our local library has already closed it's doors but for now you can still buy books online and of course there is always audible and kindle books etc.
Exercise stuff so you can stay fit and active even inside. I'm sticking with youtube (Yoga with Adrianne) but if you need a physical item in order to exercise, get it now while you can.
It's worth thinking about what you would want to have if you have to stay in your house for the next few months. There are so many more aspects to that than just food, in terms of having good physical health, mental health etc.