#1, don't panic. We ended WW2 by nuking Hiroshima and Nagasaki, the world didn't come to an end.
#2, don't panic. Nukes are very unlikely to be used in war, and have never been exchanged between warring factions.
#3, chemical/gas warfare has been used in numerous wars, and the world is still standing.
#4, biological agents (anthrax in particular) have been used in a variety of wars, yet somehow civilization survived.
With all that said, some basic preparedness measures always make sense. Storing food and water can help out not only in the unlikely event of an NBC/ABC war, but also after a fire, earthquake, hurricane, tornado, train-wreck, or other large-scale disaster.
Consider Mazlo's "hierarchy of needs".
Food, water, air, shelter, and clothes go a long way towards survival. Self-defense tools help increase your odds. Methods to communicate (or at least receive radio) with the outside world are another plus. Long-term survival tools include farming/gardening equipment, seeds, etc. Medical supplies can help ease many situations that could otherwise get out of control, too.
And one also needs to consider that "shelter" and lots of high-value stored items carry risks. Holed up in your shelter with lots of food, water, and medical supplies, you are unlikely to leave even if radiation, rogue military forces, disease, fires, or other dangers suggest otherwise. You also present a tempting "target" to desperate souls outside your well-prepared camp. Run a generator, light all your lights, and watch DVD movies while the rest of the population is starving, and rest assured that armies and hoardes of nothing-to-lose-folks will come knocking.
So remember, the odds are that you'll never need your supplies. Misuse of your supplies will make you a target, and the mental comfort provided by your supplies and shelter will cause you to resist abandoning your enclave no matter what the situation.
That being said, don't panic. Make basic preparations. Be smart, and go on about your life. There are probably still some Y2K'ers out there who are still hiding in their underground shelters, cravenly thinking that the world destroyed itself on 1/1/2000. Don't be like them.
Be prepared, just don't let it rule your life.
#1, don't panic
You cut to the heart of the matter very elegantly- NBC weapons are also "terror weapons," and one of the consequences of terror is panic, or doing nothing.
This can be countered by education and information-- and that is the first step to making these things less effective, and less likely to be used.