When I started on this baby journey I did a lot of research into the "essential" baby products out there and got what I thought would be the most useful, knowing I'd have to adjust for whatever my daughter actually ended up being into. One thing that's true of all babies: you cannot predict a damn thing about what they will like. Some kids love bassinets and sleep in them right away, others act like they are being set down in acid. Some kids want to be bundled up with hats and blankets, others will pull that shit off in the delivery room. You can't really predict it all but some things will be more useful than others.
Some things I didn't know about until after my daughter was born because for whatever reason they aren't necessarily on the "essential" lists you find unless you're scouring every blog out there. I moved from Europe back to the states, then one side of the country to the other, while pregnant. I didn't get a lot of prep time. So quite a few things I discovered through trial and error and later than other people. Live and learn!
1. Baby wraps. There are a ton to choose from so try and find a shop that will let you test them out first. Most babies want to be close to you the first few months so a wrap of some kid is, I think, a good bet. I have a Boba and a Moby.
The difference: The Boba is thicker and stretchy so it accommodates a variety of body types, you can adjust as your baby grows, and it's easy to bounce them in it which my daughter loves.
The Moby is thinner and not stretchy so there's less margin of era. But it does mean they stay firmly in place and for summer the lighter fabric can be a good pick if you're going to be out and about.
Regardless of what you choose, get two because babies spit up, pee, poop, drool, and you're going to want a spare while you're washing the other one. Trust me, I've had the experience of a baby meltdown while the only wrap was being washed. Never again.
A lot of people swear by wraps for outings as substitutes for strollers. I think they're great but there's a big BUT coming. BUT: if you're wearing a wrap and you're by yourself with a baby you're going to have to figure out how to carry a diaper bag with you. When you're wearing your baby this is challenging because you can't exactly have anything else across your body or even on your shoulder. So I tend to think wraps work best for outings when you're with a partner who can carry all the necessary items.
2. Teether toys. My daughter isn't quite 4 months yet and while she doesn't seem to be sprouting any teeth, she does like to cram things into her mouth to chew on. Having some teethers she can nom on makes things easier because during this phase babies will often stuff their hands in their mouths when they're hungry/tired and work themselves up because they don't know what they're feeling and will refuse the thing they actually want/need. The teethers help get that out of their system so you don't go insane.
3. Tubs of Aquaphor. We have so far managed to avoid diaper rash by slathering this stuff on at every change. It doesn't irritate her and it keeps the moisture out. Bonus: you can use it on dry/irritated patches, your own lips, cradle cap, etc. It's also less messy than the zinc types which, at least with my squirmy girl, get EVERYWHERE and it's a desperate game of trying to keep her from immediately sticking zincy hands in her mouth.
4. Since my daughter is a very strong, active, and wiggly baby, we had to improvise when it came to changing time recently. While a changing pad on the floor is an often cited solution, if you or your partner have back issues, it can really strain things to be going up and down like that for changes a bunch of times a day. Not to mention if you forget something and have to put them back up, get the supply, get them back down, etc. We were using the changing pad on our Pack n Play but eventually she was too wriggly even for that. A dresser or set of shelves where the top is converted into a changing area might work for other people or very young infants, but again, my kid is just too strong.
So we turned the entire Pack n Play into a changing station. When on its highest position the "bassinet" has lots of room for her to wiggle but she can't roll off or out. So I can get a change done and, if I need to, step away for a minute without fear of her ending up on the floor. And it saves my back a lot of strain.
5. White noise. There are lots of products out there for this, some baby specific, some not. We have a white noise machine in the bedroom anyway but we also got a Shusher and it's worth its weight in gold. It makes an adjustable volume "shush" sound that chills out the crankiest baby and you don't have to worry about your mouth getting tired or hoarse (yes, really). It's also portable so you can have it in any room, the car, wherever. It's based on the Happiest Baby on the Block philosophy.
6. Yoga mat and shoes specifically for standing/walking for long periods of time. My daughter prefers to be up and in a wrap over any other way of being, awake or asleep. She has a weird baby sixth sense where she can ALWAYS tell when I've sat down and starts squirming and fussing. This means a lot of standing and walking for me and it takes a toll when your baby is 15+ pounds and strapped to you all day. I also work from home so I have to be able to get things done. So I bought a standing laptop desk (cheap from Amazon), a thick yoga mat, and shoes nurses wear for all day standing. These are the only things that will save your feet and lower back.