This is one of the things that you can only do so much for. Gas masks, NBC suits and the like can only be used for limited periods of time and require a great deal of logistical support that is beyond most of us.
From a poor memory, some basic things you can do about preventing some of the effects of radiological threats:
-food and water from clean sources
-potassium iodate tablets
-ensure that you're under cover from any fallout material
-long handled bristle brushes and plenty of water to decon when moving back indoors.
I have some of my manuals outside, I'll try to look up some material later. Not sure how much would be applicable to civilians
"The Constitution was made to guard the people against the dangers of good intentions."
"A government big enough to give you everything you want is big enough to take away everything you have."