other than obvious basics, what are things that, when you were a new parent, you either grossly overestimated the need for, or ended up saving your ass that you'd have never guessed you'd need?
Feeding:
Depending how your boobs work, hopefully ya dont need bottles at all. But if you do, dont buy a bunch of em until you figure out which nipple your kid likes. Dr Brown's worked for us with both kids, but its by no means universal. If you do need bottles, get at least 8
Boobs dont work:
Find a formula that works, its different for every kid. Formula will rape your wallet forever, so play all the games with coupons and credits, and sales. If you have to go this route, let us know and peanut will walk you through the similac formula tricks for pricing.
Diapers:
Dont bother with the small sizes in bulk, kid is gonna change sized so quick in the first six months size nb,1,2 will phase out quick. Buy as needed.
Cloth diapers are good once the kid hits 6-8 months and you're only changing 3-4 a day. The washing isnt a big deal and they dont leak. Koala Mama ones from amazon are good (and cheap, dont fall for the 20 dollar a piece bum genius ones).
Clothes:
Lotsa fleece onsies with feet. The awesomest ones unzip from the bottom so you can pull the kids legs out to change a diaper without taking the whole thing off in this cold ass weather. Watch for sales. 3-5 bucks a piece is a good price.
The sleep sacks flop mentioned are good. Depends on the kid though.
Sleeping:
Pack-n-play: get one. You'll want two options for the kid to sleep, one in his/her nursery, and the other someplace closer like the living or dining room.
Rock-n-play: Godsend if the kid has reflux. Despite the safety warnings, it was the only way our first kiddo slept for the first 6 months. Always strap em into it though.
White noise: use an old phone or tablet or something, and set up a white noise app when the kiddo is sleeping. It allows you all a ton more flexibility and sleep when the kid doesnt wake up every time you open and shut a door, or roll over, or have a conversation louder than a whisper.
we like these two:
https://play.google.com/store/apps/details?id=com.siblify.holo_clock
https://play.google.com/store/apps/details?id=com.tmsoft.whitenoise.baby
The first can carry all the way up to to 4 or 5 years old, helps with sleep training, etc. Has a nice loud white noise sound.
Eating:
bibs. All the bibs. Oversized bibs. Like 30 of em.
there is so much more, but thats my initial brain dump.
If you were close by, we have so much stuff you could just have.