The only thing I specifically bring back from Japan are SoyJoy bars. Most of their snacks aren't all that.
As above, dorayaki, various senbei, dried squid, dango, motchi etc are easy to get hold of these days. . . as are the sweet gross stuff like choco pie and pocky.
The korean versions are also generally the same but half the price, often the same actual brand, just sold in korea.
You might not be able to get fish flavored processed cheese sausage or tiramisu flavored crisps, but why they fuck would anybody want that.