Many convenient stores carry underwear and other just in case items
You will be surprised to find many convenient stores carry the various just in case items like underwear, shaving goods, shampoo sets and others. If you are in a pinch and have to spend a late night at the office or have checked into a hotel without amenities, a quick trip to the nearby convenient store can pretty much cover you for the night.
All of the items (even sewing kits, manicure sets and others) are packaged very efficiently and can be a lifesaver on a overnight flight from Japan to Europe, Dubai, etc. Take a moment to go and look in the convenience store near the train station or next to your hotel and be surprised at what is offered and how the prices are so low. No need to use the amenity shop inside the hotel where items are often overpriced and selection is much less.