once again, there are no hard or fast rules. i would think 3 to 6 months worth of ANYTHING you dont want to be without for the short term. long term - be prepared to be mobile, even if its all on foot.
one situation i know i wouldnt want to be in is having a meltdown upwind of you and as you are evacuating everyone is begging for the Iodine that you have only enough for yourself. its cheap enough that several of those 4oz bottles of SSKI in different locations/households of friends and family is quite doable and they are good for probably 10 years.
the best of course is taking it daily and having a back stock for those emergencies.
4 - 4oz bottles for the price of three. each bottle has 120 grams of KI. when fukushima happened, 14 packs of 130mg pills were going for $400 on ebay. just sayin.
and one more thing - the gubmint wont have anything for you. nothing.