A tripod or some type of support for your landscape shots, as the best time will be dawn or dusk so longer apertures required which means slower shutter speeds and preferable not hand held. The gorillapod ain't bad if you want to keep weight down and isn't too expensive or lightweight tripod. The Circular Polariser suggested by AC another good idea.
http://www.warehouseexpress.com/buy-joby-gorillapod-slr-zoom-tripod/p1017697
If you finally decide on going for an ultra wide lens pick one of the tokina like the 11-16mm, great lens although personally, I'm not a great fan of them because of the distortional effect with these lenses. You really need an understand of when to use them..
http://www.kenrockwell.com/tech/how-to-use-ultra-wide-lenses.htm
http://www.digitalslrguru.com/ultra-wide-angle-lenses/
Where are you going in OZ?
I've been on a world wind tour of the state of Victoria when I went out on business, had a couple of weeks out there. Its a great state to visit, Ocean Road and the Twelve Apostles, Melbourne, Wilsons Promontory National Park, Philip Island, lots to see and do and lots of miles in the hire car with speeding fines

, they're abit hot on that in OZ