1. Instant ramen. The Japanese have perfected the art of instant ramen and elevated it into a whole new level. Look out for the instant versions of famous ramen chains like Ippudo and Ichiran. Before you pooh-pooh these packaged styrofoam bowls, you might be surprised to know that these premium instant ramen come with their own chashu or pork slices, menma or bamboo shoots, and the broth tastes pretty close to slow-cooked broth in ramen restaurants. Nissin's cup ramen have sizable pieces of vegetable and dried meat. Friends back home never fail to be surprised that there's more to instant ramen than just noodles.
2. Senbei (rice crackers) and similar otsumami (snacks). It's probably just my own impression that senbei and otsumami are healthier than potato chips. Whether they are indeed healthier or not, these make great gifts for friends and family who want to try the flavors of Japan. At 7-11 or any convenience store, you'll see a wide range of these snacks. Look for shoyu (soy sauce) flavored senbei, or those wrapped with nori (seaweed). Seafood flavored snacks like mentaiko or tarako (salted roe) flavor are distinctly Japanese too.
3. Green tea. The most common type of tea in Japan, often served in people's homes and in restaurants. You can purchase whole leaves at the convenience store, but matcha, the fine powder made from the highest quality leaves and used in tea ceremonies, is also available. You could never go wrong with giving tea as a gift. If you happen to travel in Japan at the right season, the convenience store will have a lot of matcha flavored sweets and confections (usually Autumn) and these make perfect going home gifts.
4. Ready to eat curry packs. Next to ramen, curry is a national comfort food in Japan. Ask any Japanese child what their favorite school lunch is and chances are they would say "curry rice". But Japanese curry bears almost no resemblance to its Indian origin. Japanese curry is milder and sweeter than the curries of the world. And you can take this home in ready-to-eat "retort" packs sold in convenience stores. They don't need refrigeration and can be simply heated in hot water. Make sure to keep this in your check in luggage as it cannot be brought on board the aircraft.
5. Umeshu or plum wine. A distinctly Japanese liquor made from steeping unripe plums in alcohol and sugar. It has a sweet-sour taste and an alcohol content between 10-15%. Some convenience stores have umeshu in clear green bottles and you can see whole plums inside. These make really good gifts. Sometimes though like in this photo, you can't see through the packaging. Umeshu is my favorite thing to order in Japanese izakayas (gastropub) and a flavor I like sharing with friends back home.