The shortages will be for fresh goods with a shelf life of less than a week. You can't stockpile for that.
But you can stock up on substitutes. I have a cupboards full of tins jars and packets of fruit and veg that we like.
Jars of peppers, loads of passata, pesto, pasta sauce, tins and packets of beans, pulses etc, dried mushrooms, nice herbs, tinned peaches, pineapple etc, dried apricots and raisins etc etc.
You struggle by on rations if that's what you want to do. I want my growing kids to continue to have fruit and veg in their diets, and for us all to eat food we enjoy.
It's not only fresh food that'll be in short supply btw.
Hopefully there won't be any shortages and if so great. But even if that happens, prices will go up anyway so having a cupboard stocked with food we like bought at pre Brexit prices certainty isn't going to hurt. But if there are shortages it will be invaluable.
This government doesn't give a fuck about your welfare, have you not worked that one out yet? Their ideological austerity policies cost 100,000 people their lives. What did they do about it? They made it harder to count them and ploughed on with their policies.
Don't rely on them to feed your family.