A Noelle,Stick with what you know about him. Likes and dislikes.
Look close to home. Local treats and crafts are always nice and generally not found in Japan.
I like sending gifts and have several penpals. I have sent music CDs of music I know my penpals would not get for themselves. I have sent locally made candies. I have sent books of common interests...
Stick with what you know and you will do fine.