Imo don't worry too much about clothes as the chances are you will be given more than they can ever wear anyway. I ended up taking some of my gifts back to be exchanged for 0-3 months or even 3-6 months as everyone bought me newborn outfits.
hagred's list is a good one. Buy 3-4 packs of nappies which will be loads just so you don't have to worry about it for a little while. By the time you start to run low, you might like the idea of walking to a shop to buy more, just for fresh air (if you live someone suitable for this anyway).
At the moment my DS is mostly dressed in a vest (long sleeved) + onesie/outfit+ a jumper in the day. At night he wears a soft onesie and a vest. Other than clothes buy a soft blanket for the pram/cot. In a little while you can buy sleeping bags for them to sleep in but my son was too small for these at first.
You will need tight fitting sheets for the mattress and make sure your bedding can't fall into the co sleeper (eg if you have a particularly big duvet etc).
Other than the pram, car seat, cot you've got most of the essential equipment covered but you will need a changing mat (consider a changing table to save your back too), cotton wool and after a few weeks I would recommend a baby gym/ playmat and/or chair so you have somewhere to put them down. My DS loves his vibrating chair so much I rate it as one of the best purchases we made. (We had a tiny love one - the toy bars fold back so v easy getting baby in and out and he looked so comfy in it).
Monitors- I bought a really expensive one and equally like a cheap one I use as a spare at my mum's house.
Buy muslins too- useful for everything. Baby sick, sunscreens in summer, swaddle cloths if your baby likes that, a mat to put them on when out and about.
Assuming you don't live somewhere really rural, I would recommend just getting a few essentials to tide you over for the first few weeks. I know you want to get organised pre baby but I found I made better decisions once the baby was here on what I really needed.
Eg I didn't use a baby bath for months as I felt safer ( and he enjoyed it more) in the (clean) kitchen sink.
Sorry for an epic post, I clearly have more opinions on this topic than I realised.