Ask your friend try to find some battery less emergency light with mobile charging function. You can buy made in china products also coz quality is same or near same for Japanese market. If he is in Tokyo ask him to visit Akhiabara electric town.
Sanyo eneloop recharable batteries are good too for use in torch or emergency lights.
the best thing to buy is a pile of Mosquito coil(katori senko) by Kincho. Very effective for to kill mosquito. picture attached
Kitchen lighter are very good quality too if you have not automatic burner at home. This will save matches and can be refilled. My mother's favourite.
Japanese kitchen knifes are the best as brother suggest above.
Ask him to visit 100yen shop and he will find hundred's of product which make life easy.Those product are cheap but useful for daily life. the best way to give cheap but useful gifts.
Mosquito coil (katori senko)
Kitchen Lighter (Ask him to buy god quality)