50% of our food is imported. Of that 30% is imported from the EU. It makes sense to stockpile items that are non perishable purely from the point of view that prices may rise sharply in the medium term. If we suddenly don't have deals with everyone they will be taking advantage of our situation to charge more.
Also worth bearing in mind that our farms are funded by EU subsidies and staffed with EU workers. I'm not sure how subsidies will be affected in the event of a no-deal. But it's happening around the time when farms need the most work put in to manage crops.
Of course if we have a deal none of this is an issue... But if you buy more of what you'd normally use plus some then it will do no harm. Supplies of non food items are also affected by other global factors in particular political risks and the weather. Things we take for granted such as toilet rolls and detergents are going to have inputs from various countries. I've noticed that loo roll and kitchen roll are going up in price and the supermarkets compensate by changing the product design (putting bigger rolls in). There must be various supply chain issues affecting these items.
Petrol and fuel costs could also go up overnight. Good thing it will be Spring, but it will all contribute.
It's not project fear it's common sense. It's so boring to keep seeing project fear all over the place when companies are making a big fuss about their situation and politicians don't know what to do next. Fact is we are in a shambles and it makes sense to plan for what comes next even if it works out at the last minute.