They in turn will return a gift and thus you have established your arrival on a friendly note. If you go away for a trip, even just for a day, bringing back some small souvenirs of the visit for your colleagues will be greatly appreciated. This is called omiage , and is a very established custom. You are not obliged to follow it, particularly if you are making the most of your time in Japan and going away every weekend, but it will go down very well if you do. If you are invited to a Japanese family s house, then always take something with you to give to the hostess.
Flowers are ideal, or some nicely presented food.
I can guarantee that wherever you buy a gift, the staff will wrap it beautifully to a standard and a style I have never seen in the West. Do not be offended if your hostess does not open the gift in front of you. It is the height of bad manners to open the gift immediately. Likewise, if you are given something, you should observe the same convention. Still, as a foreigner, it is quite likely that you will be urged to open it at once.