I made the mistake of not buying many little (nb) clothes, and ended up having to buy some in the first week out of hospital!
The best things for us were:
Cloth nappies - for all the reasons noted already. We still use them for loads of things, I always have a couple in the car to use at the supermarket in the trolley, or for temp playmats, or change mats..etc...etc...
MB Carrycot that went on our buggy frame - great for walking when he was little, and we used it for daytime sleeps (as he wouldnt settle in the basinett during the day).
Our Safe-T-Sleep....fantastic for knowing that he is going to stay in one place in the cot!
Wraps - my mum made me some big muslin ones, fabric from spotlight, much cheaper than buying them.
Moniter - we got a phillips one with 2 receivers, so we have one in our bedroom and one in the lounge!
Change table, mobile, play gym....think everyone has covered it!