Bread, milk, eggs, rice, batteries, toilet paper.
Actually, I think milk will come of this list of things that are hard to find in stores. They found trace radioactivity in milk from Fukushima about two days ago, so you just know people are going to stop buying milk from Hokkaido...
Something to add to the list: diapers (for both babies and adults) and feminine hygiene products. I've got 1 1/2 packs of diapers for the Pumpkin Prince in the closet, and I expect things will have died down by the time I need to get more. I can deal with the lack of feminine hygiene products if that pack of sanitary napkins went to some poor girl sleeping in her school gymnasium, but somehow I think it went to some local lady who tossed it with about 10 other packs of sanitary napkins in her shopping basket because she "doesn't know when she'll be able to find them next".