First off

get a Gieger counter NOW …. you can get cheap ones that will do well enough that plug into the audio jack of a cell phone  .. and cost under $35.

Decide whether you will  bug in and convert a basement room into a bunker, or setup a bug out fall out shelter far from your home either way You will need to invest in a large amount of strong plastic drop sheeting.

Invest in gas masks for the whole family, and other protection gear as you might need.

Invest in a positive pressure fan system and HEPA rated filter for the safe room/fall out shelter.and a solar setup to run the fan 24 hours a day

Good instructions for use and why you need it here: http://www.alpharubicon.com/basicnbc/safefanwar.htm

Store enough Food and Water for at least 2 weeks – preferably 6 months.

get a pile of empty sand bags and good shovel.

get your latrine requirements sorted out .