Well it will be more than just a bright flash, it will be a thermal flash with intense heat. What you wear day to day (assuming there is absolutely no warning) could prove the difference between live and death. Polyesters, nylon and other synthetics may well ignite or melt into the skin. Wool clothing will help considerably. Many will be blinded etc. Many folks won't instinctively duck and cover for the blast wave front.

The blast wave will destroy quite an area of property much depending on the construction. An air burst will generally destroy more property than a ground burst. A ground burst will generally generate more fall out.

Protection from fall out is best shown here;

http://www.youtube.com/watch?v=m6U9T3R3EQg



Typically staying in the protection shelter is 10-14 days. An NBC suit and respirator could prove very useful and can be had for less than £100. A portable Geiger counter would be useful as well for measuring the intensity of the fall out and its decay rate over a period of time.