Hi Icedig. The best clothing is what you would normally wear for cool weather: jeans, flannel shirts or sweaters, etc. The parkas and such you’ll get at the CDC (clothing distribution center).
Yes, you can mail stuff to yourself — just don’t expect it to get there anytime soon. I’m still waiting on coffee, books, and some spare clothes… The shipping address is in California, so shipping costs are reasonable.
Don’t mail any perishable items because they’ll spoil before they get there. (Someone once sent a Big Mac and Fries to a friend as a joke, and by the time it arrived it was, well, unrecognizable. ‘Nuff said about that.)
Things that you won’t need until after you leave the Ice can be left at the CDC in Christchurch. I leave my scuba diving gear there; others leave backpacks, luggage, bicycles, etc…
My suggestion is to travel light. Send a care package or two to yourself, just for the fun of it, but don’t feel like you have to send the house. You’ll thank me at the end of the season when you have to pack it all up again.