Assuming that I didn't die of starvation, disease, radiation poisoning, wild animal attack or being murdered by marauders, I'd establish a new ruling dynasty with myself as king. My aim would be to preserve as much of the cultural and scientific achievements of the pre-war civilisation as possible, and to that end I would gather together all of the surviving books that I could find into one big library. I'd build a society based on a love of knowledge and learning, respect for the natural world, and respect for one's superiors, coupled with a sense of strong obligation on the parts of the elite to the lower classes. Since this is presumably occurring in my home country I'd seek to preserve British traditions; in particular I'd attempt to revive and preserve the Church of England, which would also provide a strong religious incentive to obey royal authority, and form a parliament to which all of my subjects would be able to elect representatives to approve new laws and taxes. I'd also promote the teachings of Confucius, in particular his views on learning, government and the importance of ritual and proper social relations, which together with a strong Christian morality and a sense of civic duty would provide a stable moral foundation for my new civilisation. The culture of the new world would be influenced by my own personal interests. I'd combine elements of Medieval European, Classical Graeco-Roman and Imperial Chinese culture that I liked. A strong military would be a must in order to protect my civilisation from rival groups. Because feeding everyone would be the most immediate concern, society would be principally agrarian with each family group being granted a farmstead. There'd be a small town to serve as my capital, with the most talented and/or intelligent children being given the opportunity to join the bureaucracy or the military to help administer or defend my country.
I'd leave behind a charter establishing the inalienable principles of law in the new state- things like innocence before proven guilty, the right to a fair and open trial by jury, etc. This charter would also dictate the terms of succession, which would take the form of absolute primogeniture. It would also give parliament certain prerogatives such as the right to veto new taxes and establish a regency if the monarch is unsuitable/incapable of ruling. The nobility of the new state would be made up of talented ennobled individuals and their descendants, and the economy would be a distributist guild-based system.
Alternatively, I would track down Infected Mushroom and together we would build a society based on that of Westeros in Game of Thrones, with myself as the founder of House Stark, Warden of the North and Hand of the King. Thus satisfying both IM's bizarre obsession with GoT and my nostalgic desire for a romanticised, pre-industrial monarchy.
