A lot less than most people think!
You need:
Sleeping
Somewhere for baby to sleep (this can literally be a box as in the baby boxes) but typically it's a choice of a next to me, a Moses basket, co sleeping or can go straight into a full sized cot.
Bedding, modern trend is for sleeping bags but blankets worked well for millennia and one size fits all.
Transport
A car seat is a must if you ever travel by car, you can get ones that can be lifted out or ones that stay in the car, there's pros and cons on both
A pram, pushchair and/or baby carrier. You'll need something but at first you can keep it simple until you work out what works for you - and second hand/borrowed is a great idea at first.
Nappies
At first it's usually easiest to use disposable because it's such a short time they need the tiniest ones and you'll be tired and adjusting. Afterwards there's lots of options for reusables and they save money, especially if you have additional children.
Clothes
At first it's easiest to stick with bodysuits and sleepsuits, plus cardigan if you have a cold house. If midwinter you may need a warm snowsuit but again if you can get second hand i highly recommend because I rarely needed it. You don't need many of the above by the way, 6 is plenty if you have a washing machine and tumble dryer, perhaps a couple more if you don't have a dryer. You do not need fancy clothes yet.
Other things
Muslin clothes - at least half a dozen
If breastfeeding, get reusable bamboo breast pads and buy a sleep bra and a nursing bra very close to your due date (get one only of each at first as you may change size up to 2 weeks postpartum or so)
If bottle feeding you'll need bottles, steriliser etc but I'm not up on the options as I breastfed mine