Last year I uploaded a series of printable cards for communicating dietary restrictions in Japan. This is a follow-up of sorts to this, with some information about food package labelling and allergy-causing products.
There are seven substances that must, by law, be indicated as being present on packaged foods that contain them in Japan. I've listed them below in this order: English: kanji: hiragana or katakana: roma-ji.
A selection of print and cut cards to communicate your dietary requirements and restrictions in Japanese. I've edited it to add some more information about food product labeling.