Though not the first priority in a survival situation, food is of course essential to both short-term comfort and long-term survival. Food provides the body with energy for movement, fuel for the brain and a long list of components needed for cell life, repair and growth. The bulk of the energy requirements are provided by carbohydrates such as starch from grains and fats such as oil from pressed seeds though of course multiple sources of each are available. The body needs numerous nutrients other than purely energy with some 'micronutrients' necessary only in tiny amounts but, if missing, leading to health complications.    . Once shelter, water and security have been established, food then is next on the list.
Energy is typically measured in Calories (often written as 'kcal') with a typical adult male requiring 2,500 kcal and a typical adult female 2,000 per day. Since more kcal are consumed when doing heavy manual work these figures are only a guideline, the British Navy quote up to 4,000 kcal daily for those undergoing military training. Prior to understanding of overall nutritional needs, the mistaken belief that bodies need only energy led to Scurvy in sailors and the curious "rabbit starvation" condition brought about by eating only lean meat. Energy by itself is not enough for long-term health.
Modern understanding of nutrition recognises the need for a varied diet to maintain health including, for example, the requirement for undigestible fibre in food for bowel function. A healthy individual can survive for the short term on an unbalanced diet but planning for the long term requires taking balance into account. It's worth noting that some diseases which were a scourge in earlier times have been essentially eliminated in the developed world through mandatory food fortification and without that, conditions such as rickets and goitre could be more common.
In any disruptive situation food and fuel stocks tend to be rapidly depleted, the situation made worse by panic buying and stockpiling once the public realise that a problem is occurring. A relatively short-lived snow storm caused significant food shortages in Ireland and the UK in early 2018 and the threat of a tanker drivers' strike panic buying of fuel in the UK in 2012.
The US Government makes recommendations on having supplies of food for emergencies though these seem strangely deficient and in general, detailed official advice seems to be hard to find.
As it's highly unlikely that there will be food readily available in an emergency situation, planning means having suitable stocks available to keep yourself alive and well for the duration of the emergency. Since it's possible to survive for several days without food before the onset of debilitating starvation symptoms - despite the discomfort of being hungry - planning needs to address emergencies lasting weeks or months. If the emergency is localised in effect one can reasonably hope that external agencies will eventually start organising relief supplies but this is likely to be hapazard and poorly done in the initial stages and slow to respond, taking several weeks before a system emerges and potentially a very long time before a semblance of normality returns. After Hurricane Irma destroyed the infrastructure, Puerto Rico took almost a year to restore power supplies.
In the case of localised emergencies, depending on their nature, an appropriate response may well be to move out of the affected area to somewhere where infrastructure is less disrupted.
Larger scale emergencies may simply be too much for anything resembling an organised response and at the point the situation becomes extremely serious An investigation of long-term food security carried out in 2008 covers the issues in some depth. It notes that not being depending on only local supplies helps to ensure multiple sources of supply, so in normal times it makes sense for nations to import food, as this dilutes the risks of localised crop failures. The problem is that a nation which depends on imports then depends on the free flow of imports. An emergency which disrupts imports raises the very real prospect of food shortages.
According to DEFRA the UK imports approximately 50% of its food stuff and:
"Crude calculations suggest that UK agricultural land could provide more than enough food from arable production in terms of our daily calorific requirements, in theory making the UK self-sufficient.
In the UK self-sufficiency ranges from around 10% for fresh fruit to around 100% for cereals. As a measure of domestic food security, self-sufficiency does not cover the processing and distribution of food, it does not allow for the imported energy on which domestic agriculture is directly and indirectly reliant, and it does not take account of the resilience of the supply chain.
Even if it were possible, self-sufficiency would not insulate us against disruptions to our domestic supply chain and retail distribution system. It would open up the UK to risks of adverse weather events, crop failure and animal disease outbreaks. We would continue to depend on imported fertilisers, machinery and certain foods for a balanced diet. Similarly, our food chain relies on various forms of energy, much of which is imported, so ensuring our energy security is as much of a priority."
The report does note that the self-sufficiency argument is largely theoretical as it would require the population to switch to a vegetarian diet and does not allow for a simultaneous breakdown in oil supplies: UK agricultural production is highly mechanised and dependent on oil for tractors, also on fertilisers. If we are unable to import food it seems highly likely also that oil and fertilisers will be in similarly short supply.
In the case of serious breakdown of normal food supply chains on the larger scale it is hard to see any outcome other than extreme hardship, starvation and death. After the second World War, the UK kept some strategic food stocks in large depots which were disposed of in 1991 and there is apparently no strategic food reserve in place any more.
It is clear to anyone contemplating this kind of scenario that individuals need their own strategic food reserve. This is a topic covered in depth in numerous survivalist and prepper forums as any internet search will reveal, ranging from keeping short term stores locally or at a remote retreat (since cities are liable to be hostile places following a breakdown) through to self-sufficiency by owning, farming and defending land. The quality of these internet sources seems to be highly variable and it's not clear how much information is well researched or simply rehashed by being repeated and duplicated. One source which seems reasonably credible is James Wesley, Rawles which gives practical guidance on foodstuffs, storage, volumes required, inventory recycling and more.
Survivalists such as Rawles often see a back-to-the-land subsistence farming approach as a path to long term survival assuming that recovery to a more normal societal situation may take years or longer. Those contemplating such an approach may also find the publications of the late John Seymour illuminating. His "Complete Book of Self Sufficiency" is based on years of his own experiences rather than armchair theorising. A read of that book, coupled also perhaps with his "Fat of the Land" is liable to bring a dose of reality to the view that someone from an urban background can quickly learn the skills of running a small farm. The skills may not be high technology but the breadth of knowledge and ability needed is not learned rapidly. Seymour studied agriculture and worked on the land for some years before taking up his own smallholding yet freely admits he had large gaps in his knowledge and both he and his wife supplemented their incomes by other means so they could purchase fodder and other essentials at times.
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