When I visited Japan a few years ago, I was particularly impressed at the cleanliness of its streets. No litter at all. Hardly a trash bin too. The lack of trash bin however posed a little difficulty for me. It was winter time when I was there and I had a running nose. I had to clear my nose often but there was no trash bin to dispose the soiled tissue. As I walked along the streets I was constantly looking out for a trash bin. Eventually I had to dispose them at the hotel.
Thus my advice to those travelling to Japan would be to carry a small disposable bag around, it would be useful for those little trash.