I've found Tena Lady Extra much, much better than specific maternity pads. They're more comfortable against my stitches as well and seem to stay in place much better, whereas the maternity pads were always going astray, which could lead to embarrassing moments. I had disposable knickers for the first few days. They were OK but not very comfy. Quite nice to be able to bin them and forget about them though. I've 'graduated' back to proper pants now. Highly recommend M&S 3for2 granny pants about 2 sizes bigger than you'd usually take. They're nice silky fabric so are comfy if you've got stitches and are definitely full coverage! Plus would sit high enough on your belly to cover the wound if you had a c section. They do look terrible, though. 😂
Amounts wise if you're not able to leave bits in the car I'd advise taking more than you think you might need. If you have stitches you want to be able to change them very frequently to keep them clean and comfortable and there's no way to predict how long you might be in hospital for. We've been here a week and I've gone through a whole pack of maternity pads and a pack and a half of Tena Lady and my bleeding is pretty light (the midwife even commented on how light it was and I felt like I'd won a prize 😂).
Nappies wise, we went through a big pack of Pampers and most of a smaller pack of some random brand we bought in the hospital pharmacy this week, but he's a champion wee and poo-er and has a tendency to wee as soon as we put a new nappy on him, no matter how long we leave him with the old nappy after that first blast of cold air. Much cheaper to buy at your local supermarket and bring them in rather than a panic buy at the hospital, though, if you end up needing more.
Nighties wise, I didn't have time to get one and quite glad I didn't bother as I hate them and wouldn't have worn it afterwards. I laboured in a cheap black maternity dress I happened to be wearing anyway and during transition I got so hot I told them to cut it off me (lovely, rational midwife took it off me rather than cutting it 😂) so just gave birth in my bra so that was the only thing that got messy. They got me to take my bra off once he was out and happy so we could do skin to skin. By that point everyone in the room had seen my bits and the midwife was dutifully sewing them back together so I decided I didn't really care if they saw my boobs too. You'll be given clean sheets and stuff too so can always pull them up around you and baby if you prefer and are more comfortable like that. I'm quite pleased I didn't waste money on a nightie, even if it is only a couple of pounds. I have also preferred having really soft pajamas when in NICU with him. Means I can just take the top off or tuck him down it if I want to do skin to skin and I feel more comfortable and less exposed when walking around in them. Make sure they're nice and lightweight, though, whatever you buy, the rooms are so hot!