Many of the guidebooks and such tend to mention the need to bring gifts of appreciation but they can be a bit vague as to when it is appropriate. Certainly if you happen to be invited as a guest into a private home a gift is appropriate. Often snacks or a bottle of nice booze are appreciated. But for employees doing their job, I would never consider it. Unlike in the US, service people are paid a living wage in Japan and take pride in doing their job well without the need for a "bribe."