Look for babygrows that have the little flaps that you can fold over instead of mittens, so much easier. Get around ten in a combination of newborn and 0-3.
You'll need around the same amount of vests. Probably three or so cardigans and some hats.
At least three Moses basket sheets, and make your mattress up with two at a time. Gives you extra mattress protection and you can quickly whip the top one off in the night if you need to.
Size 1 nappies, plenty of. At least 6 packets of baby wipes. Cotton wool and flannels are also an essential. More muslin clothes than you think you'll ever use, at least ten, and get the giant ones if you can, they make great feeding covers, emergency cot sheets, all sorts.
For you, maternity pads, giant supermarket knickers that you won't mind throwing away, plenty of nighttime unscented sanitary towels. Breastpads and nipple cream (don't scrimp one these, your tits will thank you).
Cheap slippers to wear on the maternity ward, I threw mine away in the hospital, there was no way I'd wear those on my own carpets. Cotton dressing gown is nice to have too, lighter the better as the wards are usually sweltering.
Also, there's no harm in stocking up on calpol, nurofen, teething gels / crystals and infacol prior to birth. There's nothing worse than needing these things and not having them. A decent digital thermometer is good one to have to.
You'll probably be gifted a gazillon blankets, most of which will be completely unsuitable for a baby to sleep under. Get sleeping bags, just check the weight guide on them.