Don't talke in loads of crap becasue you won't need it. I bought some mini shampoos/conditioners/shower gels, you can get them from boots for a couple of pounds. They are much smaller and fit in your bag better, plus they were ideal for me as I was only in for 3 nights. If you end up needing to stay in hospital for long periods of time somebody can bring you in more supplies.
I had a cheap nighty bought from Primark to labour in, and then a nighty that had easy access for breast feeding. I also bought a very lightweight cotton dressing gown from Primark for about £6.00. Although the post natal wards are very warm, I found it a bit embarrassing getting up and going to the loo, for breakfast etc when other family members were around. So my dressing gown was light enough that it didn't make me too hot, and meant I was 'decent' in front of visitors etc.
On me second night I asked my mum to bring me in a lightweight pair of PJ bottoms though as I was bleeding very heavily and was worried about any spilage whilst visitors were in. They were again, lightweight, baggy and elasticated which meant they were easy to slip on and off. Rememeber when buying things that you may well be in pain after the birth so having to faf about with buttons, ties, poppers etc may not be ideal. Try to find things that are easy to get on/off, undo and whip down when you need to pee. Try to get things that are dark colored to wear, becasue if you do have any accidents, it wont show. Though by this point I was so far past caring if I had any dignity left it didn't really bother me lol!
Don't buy disposable knickers they are CRAP! Go into Primark and get some cheap black cotton granny style briefs. They're about £2.00 for a 5 pack. I bought 2 or 3 packets and they were the most comfortable things ever. Plus they were so cheap it didn't bother me to throw them out. My disposable knickers from Tesco's cost much more, they were the most uncomfortable, itchy things ever! Good luck