How do I post a box overseas from Japan?

I would like to post a box of lugguge to Australia from Japan, and I want to know the cheapest way to go about it, or more simply, what options exist?

go by boat. But send the things you won't need right away because it'll take like a month to get there.

Send it Funabin but be prepared that it can take months to arrive. I have done this several times with books I bought in Japan.

(..) take months to arrive
To be a bit more precise: Once to France it took 3 months and once to the UK it took 6 weeks. Still, I think it is great, cheap option for stuff you don't need right away.

If it is only books, there is a book rate at the Japanese postal offices that is cheap.

If your parcel is under 2 kg and measures no more than 90 cm on all three sides, you can send it as a small package:

http://www.post.japanpost.jp/int/service/small_packing_en.ht...

or if larger, regular surface mail parcel. You can check all the options and prices here:

http://www.post.japanpost.jp/cgi-charge/index.php?lang=_en

After the small packet option, a parcel of around 4 kg and above will give you the best value per kilo.

Note that you will have to supply detailed information of the contents on the customs form and may be required to pay customs charges when the parcel is delivered in your home country. I would suggest that you get this before taking your parcel to the post office and have it filled in when you return with the parcel.