Let me preface this dissertation by saying that not only am I a mom to 4 kids, but I am also a certified natural childbirth and breastfeeding instructor... so I have a lot of personal experience as well as professional. So, this is probably WAAAY more than you really wanted to know... LOL!
First of all, a few thoughts... go ahead and start your prenatal vitamins now, start doing mild conditioning exercises like walking, cut down on caffeine, quit smoking (if applicable) and limit your alcohol consumption. Basically get your 'body' house in order BEFORE getting pregnant - that is frankly more important than getting your house ready for a baby. It wouldn't hurt to get the future dad on a good multivitamin, and have him cut down on nicotine and alcohol consumption (if applicable) as well to boost fertility. A good pair of boxers can help too.
Now, for the 'stuff' you need...
Disposables - a newborn in the first month will go through about 10 diapers a day. Don't buy too many size NB or 1s though, because they will outgrow them very quickly. Plus if you get diapers as gifts, everyone tends to buy you the smaller sizes so you have more than you need for the first couple months - that goes for clothes too...
You can never have too many wipes...you'll use 1000s of those through toddlerhood and beyond!
Here's a suggestion - rather than purchasing actual products, buy youself gift cards for the amount of $$ you are setting aside. That way once the baby comes, and you know more what you really need, you'll have the money ready but won't waste buying the wrong things or sizes etc.
The absolute BEST baby shower I had was one the lades at the church threw for me. When they asked me what I needed, I asked them to make the theme the 'Disposable Baby' shower. Everyone who came was asked to bring something disposable - ie diapers, wipes, paper bibs, etc
I didn't have to buy diapers at all until my baby was over 6 months old.... AND you can always exchange almost anything at
Walmart if you get too many of the wrong sizes.
As a mom of 4, I've definately been there and done that, and can tell you that I bought WAAAAYYY too many gadgets for my firstborn.
For me, the necessities were a swing, stroller and a carseat, a few changes of clothes and diapers/wipes. AND, I recommend you get the lightest weight stroller you can get - some of them have a bar that you can attach the car carrier to, rather than getting the big huge combo sets. Those things weigh TOO much!
Now for some more *free* unsolicited professional breastfeeding advice:
I would highly recommend NOT having any formula or bottles in your house. Studies have compared women who had formula vs women who didn't who expressed an equal commitment and desire to breastfeed. Those who had formula 'just in case', or received samples from their Dr office, or even were given 'pro breastfeeding' materials sponsored by formula companies are significantly more likely to turn to the bottle and quit breastfeeding. Formula companies spend millions of $$s on marketing because it REALLY WORKS to get babies off breastmilk and on formula, despite their undeniable admissions that 'breast is best'. If 'they' could put the benefits of breastmilk in a pill or shot, it would be mandated by law for the health of your child. But because there isn't much money to be made from feeding your baby the vastly superior food as God and nature intended, that won't happen. Breastfeeding is the MOST IMPORTANT thing you can do for the long term health of your child, even if it is just for a few weeks.
If for some real reason, breastfeeding isn't going well, let me recommend you see a lactation consultant - LC - (the hospital or Pediatricians office should be able to recommend someone) AND check out your local La Leche League. If the LC you find seems more interested in pushing the bottle than helping you resolve any issues and keeping the baby on the breast, you have the wrong one - ask to see a different person. If you truly have a need to supplement, then it's not like the grocery store is in the middle of nowhere. Most areas have at least one 24 hour store so you can get formula and bottles within minutes if you really end up needing it.
I highly recommend the website
www.drjacknewman.com. He has solid wisdom and insight on how to achieve breastfeeding success. He has a $30 video available. Instead of buying formula, spend the money on that video. I assure you it will help you get off to a good start. I make it mandatory watching for my students and also send home each of them with a copy to keep. If $30 is too much, send me a PM and I'll send you a copy myself - that's how much I believe in his methods. I've seen his techinques work MIRACLES for women whose babies were not thriving and who believed they didn't have enough milk, etc.
Ok, off the soap box now...all the best on your pregnancy plans!