Suggestions on food/snacks to pack when travelling with celiac to Japan

My husband and I are traveling to Japan in a few months. He has celiac disease. Due to the prevalence of gluten in Japanese food, we anticipate not being able to eat out much, if at all. What are some food items that are easy to bring along and eat, assuming we have access to very basic cooking facilities?

I've read a lot of blogs about traveling in Japan with celiac disease and the more I read, the more difficult it seems eating out in Japan will be. Gluten seems to be everywhere from the more obvious stuff like bread and cakes to more surprising things like soy sauce and some teas. Even things like edamame (which are naturally gluten-free) are sometimes boiled in the same water used to boil noodles, so the risk of unknowingly eating something that is cross contaminated with gluten is very high. We will be carrying a travel card like this to help explain what foods are dangerous to eat to restaurant staff, but we don't anticipate it making eating out completely safe.

We will be staying in various cities across Japan for about two weeks and will most likely be renting small apartment AirBnBs for a couple of days at a time, so we will have access to a kitchen. However, as apartments in Japan are so small, kitchens often consist of...a sink and a hot plate :)

We don't really want to eat protein bars for 14 days haha, so I'd really love any suggestions on things to pack. Obviously, nuts/trail mix, the aforementioned protein bars, and even a loaf of Scharr's gluten free bread (which unlike other gf breads, doesn't require refrigeration) are already on my list. We should have access to grocery stores for things like produce. (But since celiac is so rare in Asian countries, the store will be unlikely to carry specialty gf items, like bread.) I will also probably pack some gf instant noodles.

Thank you for your suggestions!

Source: Suggestions on food/snacks to pack when travelling with celiac to Japan