I think there is an obvious solution to the effect fallout would have on soil and your ability to produce food.
Assuming you have time to prepare some land before the event , you would do so by rolling some black plastic film out to cover your best garden soil , cover it with an inch of soil or sand so it wont blow away , wait 3 - 6 weeks after the event for fallout to cease , put on your mask and booties and push the plastic back to allow use of the protected soil underneath for growing your food.
You still need a source of clean water , hopefully you have an underground spring you can pump from until the rivers are clean.
Assuming you have time to prepare some land before the event , you would do so by rolling some black plastic film out to cover your best garden soil , cover it with an inch of soil or sand so it wont blow away , wait 3 - 6 weeks after the event for fallout to cease , put on your mask and booties and push the plastic back to allow use of the protected soil underneath for growing your food.
You still need a source of clean water , hopefully you have an underground spring you can pump from until the rivers are clean.