Food labels are your best friend! Research the foods that you can't eat and make sure you recognize every possible way it can be written in Japanese. You don't want to take any chances! Check the food label and make sure it is safe before buying it.

If you're at a restaurant, make sure to tell them what foods you can't eat! If not, they might not recognize it as an allergy and think you just don't want to eat it (which is totally fine, but they might have it in other parts of the meal too). Some foods like fish stock, dairy, and soy products are not very obvious so don't forget to ask about that too. And one thing about fish! Fish is often not considered a "meat" in Japan, so be careful!

If your diet is very strict, maybe try cooking instead of eating out - you'll save money and be at ease knowing your food is safe! :)