Just make sure everything is well wrapped and protected. Things tend to get banged around. Buildings in most parts of Japan are without central heating and insulation. Classrooms are overheated in winter, while hallways, bathrooms and gyms remain icy cold. You'll probably be riding a bike to work in all kinds of weather.
Most social functions are held right after work, so there's no time to change.
You'll also be sitting on the floor a lot, so choose comfortable clothes that don't wrinkle. Clothing in Japan is expensive, sizes are small, and materials are often synthetic. Washing machines are rough on clothing, so be careful with delicate fabrics. Dryers are rare, so cotton tends to wrinkle which is a pain to iron, especially in Japan. It's also good to have a dark coloured outfit, preferably black, for weddings, funerals, graduation ceremonies, etc.