I took the advice of other moms and made a huge stockpile of diapers. I had a whole closet full and I regret that very decision. Here's the thing; how do you know just how fast your child will grow out of newborn, size 1 or 2 diapers? You don't. My 5 month baby is already in size 2, almost size 3's. She was only in newborn diapers for a month. She was only in size 1 diapers for 2 months. She's 16 pounds so she's big for her age. She was weighing at 6 month stats when she was only 4 months of age. Some babies stay in newborn diapers for a long time so you still have to keep buying diapers even though you have that huge stockpile just waiting. I do think stockpiling is extremely important, just not so much for diapers in large quantities of the same size. Babies growth only starts slowing at around a year old so it's hard to say what size diapers you should have more of. Also another thing to think about is that breast-fed and formula-fed babies grow at different rates. Formula-fed babies typically get bigger at a faster rate.
Wipes is a whole other story. I didn't stockpile enough wipes and you really should. When you think you have enough wipes, you don't. Coupons.com has a wide variety of coupons dedicated just for diapers and WIPES.
Ha, I still have baby clothes that still have tags that Shiloh never worn or even tried on. She also has size 2 shoes and she's still in size 1's and newborns even at 5 months. Buying baby clothes is definitely a money waster if you buy too much at once. MAKE SURE TO KEEP YOUR RECEIPTS.
Shampoo and baby lotion is a definite yes. I have MANY bottles because I know that I'll be using the baby shampoo and lotion for years. The best brands to stockpile for hygiene is Johnsons and baby magic. (Baby Magic is my favorite.) When baby shower time comes, I would specifically request these to help the cost of stockpiling these along with other items such as the clothes, wipes, and diapers. More they buy that's actually useful, the less out of your pocket.
For some people, it's a popular idea to stockpile bottles. I think it's a waste of money to have lots of bottles. My reasoning is that a typical baby around 6 months will transition to a sippy cup. Up until then, a baby will only take 28 to 32 ounces in a 24 hour span. After that, the baby will be supplemented by baby food after the 6 month mark. I think most mothers should have 5-6 bottles max. This also differs from breast-fed and formula-fed babies. If you are primarily breast-feeding, you would need fewer bottles (maybe 3-4 max) until other circumstances appear. This is how many bottles that worked/is working for me:
3 (4oz) bottles (I used the avent brand)
2 (9oz) bottles (Also the avent brand
1 sippy cup (Yay! My baby is getting so big)
My baby doesn't need that many bottles because she's already been eating baby food at 2 months (slow process) and is staying fuller for longer periods of time.