Big high waisted pants in case you end up with a c section. You'll need pants that sit well above your wound. I made the mistake of not buying high waisted and had to send my mum off to M&S!
Bluetooth Earphones - wards get noisy and it's nice to be able to zone out with your baby during the night.
Dressing gown - your pjs can easily get stained and it's nice to throw something on over the top if you need to walk to the bathroom etc.
Water bottle with a straw.
Wet wipes (for you) in case you struggle to get access to a shower (if your DP is there throughout then you'll be grand. But I was alone when he went home and basically couldn't shower coz I couldn't leave or bring the baby)
Make sure any nightwear you bring is light - hospital wards are hotter than the sun, even in winter, you won't be wanting thermal pjs!
For the little one, if you can get sleepsuits with zips they're so much easier for middle of the night changes when you don't have a lot of light.
My throat was killing me due to gas and air, so maybe lozenges would be a good shout.
Then all the obvious stuff like pads, lip balm, snacks, charger, hair bobbles, flip flops, toiletries...
I was in hospital for 2 days in labour and used absolutely nothing from my bag. After my section I was in for about a day and a half and only used the things listed above.
Good luck when the baby comes!!!