See, I got Tourist, but I take exception to some of the answers and questions.
For example, while the human body may under normal circumstances require 8 glasses of water a day in order to function correctly, in a desert or arid environment such as would be thrown up by nuclear fallout, that can increase to needing 20 glasses. Equally, if your body weight is higher you need more water, but then you would have to account for the inevitable weightloss of being stuck in such a harsh survival condition.
Also, while technically nuclear fallout disipates after two weeks, radiation levels can still be high enough to cause severe concern to a normal human being, and depending on the prevaling wind the fallout could be cleared the blast point in under a week but cause widespread damage over a different area as it is spread, often lasting for several months at lower levels but still causing hazardous conditions.
I still maintain that I would do very poorly in a survival situation of this nature, but I've had to research this exact thing for a post-apocalyptic story project for next year, and a lot of these questions have some very serious flaws based around not accounting for the crisis situations which affect primary judgement. For example did you also know that you can survive for three weeks without food as long as you have water, but in the condition of not having either a clean water supply or a regular water supply this can be dramatically reduced depending on individual body tolerances (metabolism, predeliction to weight gain or loss), so that some people would barely survive three days, whereas some would manage a week and a half? In these situations fat people have a distinct advantage in the initial days following a global crisis, since by the time things have settled, all the thin people are dead, whereas the fat people have not only survived by drawing energy from their body weight, but the weight loss means they are now in the perfect position to start living in the new world.
I find the thought of an apocalypse fascinating. If you don't, don't bother reading any of the above.