Congratulations! I have a 9 month old baby and it tooks us over 6 years to get pregnant so I completely understand. We probably went a little bit overboard but I don't regret it one bit

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My recommendations: Start with a list of the things you NEED, and a second list of the things you WANT. Ask around to find out what you can borrow, then update your list. I started with the biggest things - carseat (Graco SafeSeat), crib, dresser, pack-n-play, stroller, etc. It will also help if you can start thinking now about where baby will sleep for the first couple of months or so. I didn't think we needed a bassinet, but my sister loaned me hers just in case and we used it ALOT and for a long time.
Yes, some people will say that you don't need much and that is true - however, there are many items that can make a very busy day much easier. For example, we debated about getting a Bumbo but I'm so glad we did! DD is still able to use it and I was able to put away groceries yesterday while she was content and in one place.
Someone has already mentioned the Baby Bargains book and website - very helpful especially to get you started and an idea for budget. As far as buying ahead of time, make sure that you are familiar with a store's return policies. Babies R Us is horrible unless an item is on your registry. My local store would not allow me to exchange an unopened box of their brand diapers because it had been over 90 days. I even had my receipt!
Speaking of diapers, I HATED theirs. DH and I decided when we were pregnant to go with Huggies, so we stocked up and stocked up and stocked up. Um, they caused DD to have diaper rash. Sooo, it took quite a while to return all those and exchange for Pampers. Luckily we bought them at Wal-mart. Moral of this story is to wait to see which diaper will work best for baby after the birth. I now recommend to purchase gift cards instead, such as getting a $10 or $20 gift card each time you get groceries. Plus it gets you a bit used to the extra grocery bill!
My friends had warned me that we would get tons of clothes at our shower (which we did), so try to avoid buying clothes until after the shower. You can purchase clothing for as the baby gets older, such as 9 or 12 months, but you have to make sure to account for which season it will be when they are that age.
Okay, I think that's probably more info than you needed so I'll stop for now.
Have fun!