I stocked up on clothes from 000 upwards, if they are too big they'll be ok, but you can't squeeze a baby into too small clothes IYKWIM. My mum went out shopping the day after Zander was born to get some 0000 clothes cos he was a little shortie LOL.

As for nappies, I'd stock up on newborns. KMart, Target, Coles, Woolies etc will allow you to change to a siz up if you need it later on. If you know the sex of bub you can try to stock up on bigger sizes though.