I think the most likely outcome is price rises, particularly of fresh fruit, and the odd supply blip of particular items, so I'm making sure my cupboards are kept well stocked. I have family abroad who routinely prepare for being snowed in for a couple months, so I try to ensure I have enough for a couple weeks in comfort, usually in case I'm too ill to sort out food.
And similarly, it's likely to be a couple days if there are other infrastructure problems. We have a gas camping stove in case of power failure, and I have reasonable stocks of meds, so its only disruption of water that could be a problem - which Thames Water had this winter anyway. I also remember the fuel crisis as I had to move house during it - no van so did 8 trips on the Tube across London, and then managed to dismantle all my furniture and get it into a taxi with a roof rack...
There will robably be a move to a rationing-type diet only with more sugar and dairy and eggs, simply for cost reasons. I very much doubt it will be like Venezuela about 5 years ago when the average person lost 10% of their body weight and on the whole, public health experts were delighted.