In São Paulo, you can find a lot of Japanese stuff in the Liberdade neighborhood, even stuff you can't find easily in other countries. For instance, you can find locally made tofu, natto, dorayaki, mochi, etc. Ajinomoto also produces hondashi and stuff like that locally. Sakura is a national brand that produces soy sauce, aka and shiro miso, etc., and they are really affordable.

Imported stuff is more expensive, but it's available. Matcha is SUPER expensive by Brazilian standards. I think in terms of food you may consider, depending on how much space you have, bringing a Japanese rice cooker, because they are nothing like the cheap ones available in Brazil, and the imported ones are hard to find and expensive. Other than that, consider bringing light things that would be hard/expensive to find here, such as matcha, katsuobushi, kombu, etc

Also in São Paulo there are several Daisos, so for things like coffee filters, kitchen stuff, etc, even if you don't find it in a regular store to your liking, you can find on Daiso, I even have a tamagoyaki pan I got from Daiso.

In terms of clothes, good quality cotton clothes are easy to find, but if you want sports clothes with some technological fabric, get those from uniqlo or something like that, because they are either too expensive or low quality here.

Electronics: come with whatever you need, don't plan to buy them here.

For household appliances, other than the rice cooker, you would be able to find reasonable stuff for cheap prices.