Bring your Nintendo 3DS to Japan. Bring it.
My daughter Amanda has carried her 3DS with her on many trips, and of course it is nice to have on the overseas flight, but... the best, most fantastic part of all is using Streetpass and accessing the Mii Plaza feature while you travel across Japan!
In the USA, you are lucky if you pick up the Mii persona of some random 10-year-old at Taco Bell, whereas in Japan there are thousands of people you can connect with all over the country.
You can carry your 3DS for weeks and not connect with anyone here, but in Japan you catch people everyday, and they are not all children but a diverse assortment of people.
If you see someone holding a game and they give you a meaningful glance, the person has likely received your Mii (it says "You've received a new region - California!") and if it seems appropriate, you can even start up a conversation based on your shared interest in games.
The E3 Convention is finishing up here in Los Angeles, and Nintendo plans to tweak Streetpass for the USA, but I doubt whether the feature will be as exciting here as it is for a visitor to Japan.
Compare "Oh, I got Utah today," to "I got someone from Hokkaido, Okinawa, Shizuoka, Chiba, Kumamoto, and Mie just from passing through Haneda Airport!"
Inside Track Japan For Kindle