Chocolate... very high in magnesium, Magnesium is needed to transfer calcium to the bones. When you're depleted in Calcium your wonderful brain goes 'hey chocolate, where are you?" One of the reasons many women crave chocolate while pms'ing.
As for the sugar cravings... just as Glaun said.. easiest thing to turn into energy so the brain will crave it, the more you give it, the more it craves it.
If it is a plant, eat it, if it comes from a plant, don't!