For small items (stickers, CDs, Candy, Games)  "airmail small packets" is pretty cheap and fast but has no tracking number up 100g is ￥240　
You can see the rates to Oceania, Middle East, North America, Central America and Europe here (sorry I do not know where in the world you are):
http://www.post.japanpost.jp/int/charge/list/normal2_en.html#

As far as gifts for girls, it depends on what she likes.
Plus if she likes a specific character, Hello Kitty etc, I can get almost anything you can imagine from plates and cups to clothes to contact lens cases. Many items are exclusive to the Japanese market.
Please let me know what your girlfriend likes so I can give you a better idea of what is available.

Thanks!