You may want to download a Japanese Language app (or several) on to your smartphone as a way to study Japanese or to help you maneuver around the streets and shops of Japan. You can search online; there are many. These following are some recommendations from past MISTI Japan interns on the types of online dictionaries and apps that people have found useful.
Before you go out shopping, to the doctor, or on another errand where you may need new vocabulary try to prepare beforehand by looking up words and preparing possible things to say. If you are going to be in the Kansai region you may want to familiarize yourself with the local dialect, which is quite different from standard Japanese. Shingu-sensei, a former instructor at MIT created a Kansai-ben self-study course that can help you prepare: Some interns have found it very helpful to learn some technical terms relevant to their field or project to hit the ground running.