This one is about omiyage, the gift of food that you're expected to bring back for your coworkers when returning to the office from a business trip or vacation. You can read more about it in this WSJ blog aptly titled "Thinking of Work While on Vacation."
During a typical week at the Japanese office where I was seconded, I would receive two to three omiyage. There are about 100 attorneys in the department and our practice was not only to bring omiyage upon return from vacation or business trips, but also to bring omiyage on our last day of work. Given that the company is constantly rotating permanent employees to and from other departments or subsidiaries, and that the secondees (roughly 1/4 of the department) are always coming and going, there is cause for lots of omiyage.
Here's a picture of my favorite omiyage from the entire year, a chocolate in the shape of Mt. Fuji (or Fuji-san, as they call it).
After a trip to the US, I brought the team Reese's Peanut Butter Cup minis because they are one of the few American sweets I've never been able to find in Tokyo. Turns out they aren't sold in Japan for a reason--my Japanese coworkers didn't seem to like them at all! If I were to do it over again, I would just pick up some Japanese sweets from the stores that carry omiyage boxes in the airport.