DMg Peacetime rationing has occurred. Post WW2 it was lifted in 1954.
How you define stockpile is a moveable feast, but I would take it at it's broadest to mean additional supplies organised in addition to what is already in the supply chain. Fuel is not imported from the EU to the UK, other than polish coal. So I really see no need for a rationing scenario to be explored. The UK tank farms and pipelines contain a strategic reserve anyway, to cover short term interruptions, should they occur.
I think the conversation is rather loosing track. We are talking a possible hiatus in EU trade, not an embargo policed by the UN. Even shipping from New Zealand or the US Pacific coast only takes around 7 weeks to UK ports. There may be a need to stockpile certain items as a precautionary measure in case alternative plans contain flaws.Personally I think the drama is vastly overstated. My feeling is that foodprices in the UK would fall unless the high agricultural subsidies are continued for UK farmers(€3 billion)
Our departure will certainly leave the CAP with a major funding shortfall and hasten it's very necessary reform.