Also beware of 全麦 [zen-mugi] (whole wheat). As for convenience stores, I would recommend you be careful with most onigiri (rice balls)... I constantly check the labels and have found that most of them have a disclaimer saying "some ingredients may contain wheat" or something like that (mind you, my reading is still not so great).
I would also recommend you be wary of the そば [soba] buckwheat noodles on sale at most supermarkets. Almost all of the brands I have checked contain wheat - it seems that the cheaper the brand the more wheat and less soba it contains. However, there is a brand that I have found in regular grocery stores in Nagoya with １０割そば [ju-wari soba] (100% soba) clearly listed on the label. I have also been able to find wheat-free soy sauce at the local su-pa.
Definitely be careful with curries... I have only found two brands so far that do not contain wheat. Look for Yamamori Thai Curry (clearly written in roman letters on the package) if you are looking for something wheat free.
At the moment I am mainly suspicious that I have a gluten intolerance and am looking for an actual diagnosis. Has anyone out there been tested in Japan? I think there must be a few celiacs around, as the wheat-free soy sauce I bought mentioned something about it being for people with a "wheat allergy."
I am thinking of doing a 人間ドック examination soon in Nagoya and getting everything checked out.