[Nyororin]

With a little bit of effort - everything.

Japan isn`t too big on "processed" things like the US - you can buy delivery pizza, and hot dogs... But macaroni and cheese would require me to buy macaroni and cheese, then combine them.
Basically, just don`t expect to find a ton of meals in a box or microwave dinners.

I quite honestly can`t think of any ingredient that I could not get access to if I were to want to make something so it`s really hard to answer your question.