If you are flying a long route in economy class, be sure to take a large bottle of mineral water with you.
Charge your laptop before departure. If it's a long-haul flight, make sure you have a charger in your hand luggage. So that you can use it on board if necessary.
Take a universal electrical "adapter" with you, as the type of socket in Japan is different from that in Europe.
Flights to Tokyo
List of popular destinations with flights arriving at Tokyo airports