After living in Japan for a while and moving back home, you miss a lot about Japan. Here are some ways to get the Japan magic back in your home country.
Tasty gyudon by verygreen
There are a good number of Japanese restaurants in most major metropolitan areas. Track your local ones down and find out where the actual Japanese customers eat. Sushi places are great, but you're better off with greasy-spoons that serve dishes like gyu-don, nikujaga or ramen.
Aside from restaurants, asian or Japanese food stores usually stock a large variety of the convenience store goodies you were used to back in Japan. If you ever get a hankering for some pocky or a pocari sweat, you shouldn't need to look too far.
A little harder to come by but if you can find a bar/restaurant that serves a good selection of Japanese beers, sake and shouchu you'll be laughing. Establishments like these are also very good for making Japanese friends.
Meet Japanese People
The best way to keep up your spoken Japanese skills is to practice with real-life Japanese people. Meetup.com hosts dozens of Japanese Language Meetups groups in many of the major cities so this is probably a good place to start.
If you can track down local places that do karaoke-boxes and have a good group to go out with, getting your Karaoke fix can be a great way to relive the ridiculous nights out in Japan. Double-fisting beers on a 3000 JPY nomihoudai and crashing other boxes is optional.
Pound for pound the best way to immerse yourself in Japanese culture is to study the language. The culture is baked into the language, and learning it well means your system for understanding the world will be coloured by Japanese culture. It is life-changing and surreal. Do it!
Consume Japanese Media
Books, movies and music are a great way to stay connected to all things Japanese, not to mention improve your language ability. Manga is a good place to start with books if your reading ability isn't that great, though real books will accelerate your language acquisition beyond what you'd ever expect of yourself.
Movies are good too but it can be difficult to find ones worth watching. A good place to start is the list of Japanese Academy Prize Winners on Wikipedia. English subtitles are fine if your Japanese isn't that great, but you'll want to switch them to Japanese (or off entirely) if it's language acquisition you're going for.
Take up a Japanese Hobby
'Japanese Hobby' runs the gamut from origami and flower arranging all the way through to martial arts like Judo and Kendo. Taking up one of these hobbies will make you a lot of Japanese friends and keep you in regular contact with some aspect of Japanese culture that you enjoy.
Man up and go to Japan!
These are all quick fixes that will stave off your Japanalicious cravings for a short while, but there's nothing like touching down at Narita, being gawked at by everyone around you when you get off the train at Ueno and starting another Japan adventure. There's only so long you can wait!