About a week ago, shelves in supermarkets across Tokyo were looking pretty much like this - nekkid. One of the reasons brought up in the foreign press was that many folks were hoarding by buying up as much as they could which was true. But another reason why shelves were empty was because many factories and suppliers had their infrastructure and logistics affected by the quake meaning that stuff just was not able to get to its destination.
Milk, tissue paper, nappies, bread, instant noodles were among some of the supplies that there was a shortage of. One of the reasons why there was a shortage of milk was that two of the factories that manufactured milk cartons were also damaged in the earthquake.