Survival is a well-understood topic with numerous sources of information. A classic and oft-cited work is The SAS Survival Handbook but a brief internet search will reveal many others, including, for example, several books by Ray Mears. This is a very well-supplied field and there are many, many other authors.
In all but a very few benign environments, human survival is contingent on a number of factors. Without these, death is an increasingly rapid probability. The following points are drawn from the sources mentioned above, adding comments from personal experience of the authors.
Though not essential to survival, the mention of fire in all three points above gives an indication of its importance in most survival situations.
If you are only used to living in a comfortable urban environment (as it's expected most readers will be), it's hard to grasp just how reliant one becomes on a reliable supply of drinkable water from a tap. A hiking/camping trip where you have to find water rather than carry it is something of a rude shock. And as outlined elsewhere on this site, a significant aspect of many emergency situations is likely to be the failure of urban water supplies. This is a very important matter.
Above and beyond the essentials of survival are protection (if there is any external threat), avoidance of injury and disease, a knowledge of how to perform basic first aid and medication and also, regularly mentioned in survival anecdotes, the ability to keep going (morale) through the tough parts, maintaining the will to live.
This section of Beat the Bear provides an introduction to survival techniques. Having a basic knowledge is an essential starting point though it is probably not enough to equip you for real-life situations where survival is at risk: you need the practical skills to put knowledge to work and skill is achieved through practice. It's easy to read about the effects of cold or thirst and a very different matter to have experienced and overcome them for real.
As a side note, care should be taken after a period of starvation. Refeeding Syndrome refers to death caused by suddenly making food available to subjects of starvation; recovery is not always a simple matter.
The books mentioned above are popular sources for people who enjoy wilderness expeditions, hiking and / or camping trips. Skilled individuals can learn to survive in most conditions, but we believe that it's impractical for most people to keep those skills current unless it's an integral part of their day to day activities.
To imagine that you can live through an emergency by throwing a backpack on and taking to the hills may be a romantic notion but we think that should be an absolute last resort (despite a large chunk of 'prepper' content focusing on it). An individual living in the hills is taking a high-risk route and in a vulnerable position. It should be possible to plan and prepare for better than that, even if it's your final fall-back position when all else fails.
The majority of us will be in urban environments: these pose particular problems and the decision whether to try to sit out an emergency or leave being highly dependent on your options. Publications on the subject of urban survival are less obviously well-researched than the military/wilderness specialists and we hope to make recommendations about this subject later.
We'll start by providing suggestions related to