fast growing food

so what if you only want to bother growing food if the store runs out of it,
it is possible,
you just need food that grows fast.
radishes are a good example,
they will almost grow faster than a person will starve, 
but it is hard to live on radishes,
so boil them first and they taste just like turnips !

if you set up a mix of fast and slow growing things you can likely get away with very little stored food than if you pick all things that are long season to grow,
so think about harvest date with things and you can get away with almost a season less stored food.