Clothes, including jacket, shoes. Bring socks for the hotel room because it can get quite cold. Toiletries (shampoo, soap, toothbrush, toothpaste, comb). Wet wipes and diapers. Something that your LO usually sleeps with, so he/she can sleep better in an unfamiliar environment. Things (eg. Books/activities) for the plane ride. Water bottle. Milk bottle (formula if required. If your LO drinks cows milk, that’s readily available in Japan). Some snacks that your LO is familiar with. I recommend yoghurt melts for munching/sucking during take off and landing. Helps with change in pressure. Baby carrier/stroller. Personally prefer the former, because there’s a lot of stairs at train stations so strollers are too cumbersome. Bring baby fork and spoon if that’s how you feed your LO. Lots of places only provide chopsticks. Have a great trip!
You can get diapers at drug store easily there. Selling pamper premium merries etc. Baby food can get from drug store if you need. Bring your own pot to sterilize baby stuff.
Diapers?