Never too early to pack the bag! I packed mine in bits and pieces from about 25 weeks which was lucky because i had DD at 28 (emergency and not expected at all) and DH just had to grab the case!
I would suggest a nightie and really good slippers as a must, I also packed a set of each size tiny, newborn and 0-3 vests and baby grows because then baby would have the right size and someone could pop back and get the right size (none of which was used for a couple of months)
I tend to over plan! Makes me feel safe iyswim. Definitely food - hospital food times are pretty random and breakfast was self serve once I wasn't bed bound so for a normal delivery would be immediately. Lunch at 2 then dinner at 5!
If breast feeding you need something to get through the night!
I'd also pack a couple of days worth of your maternity clothes because you will still need them. I also brought a pillow and needed my own blanket too. The pillow ended up getting lost somewhere between rooms so get a nice bright pillowcase.
Yes take a small wheel suitcase - what if you have a c section?
I also brought my own water jug and cup because the hospital one was a bit crap and I had also read that pouring water on your nethers helps with the first post birth pee (never needed to try that, small benefits of the section)
Don't forget the maternity pads and big knickers - post birth bleeding is not a joke! I was only in 3 days after birth but I used the whole pack, breast pads too.
Phone charger and a portable battery if you have one in case the plug isn't by the bed. I would charge the battery while using the phone then use the battery to charge so that I was never without my phone.
Not having DD with me I also bought earplugs but I doubt that would apply to most people.
If you're not a planner like me I actually wouldn't worry so much, if you forget stuff it's only a day or so and you can always get people to bring stuff and if you're in longer you can also get people to bring stuff!
Tldr: nightie, and pajamas, slippers, maternity clothes, vests and onesies for the baby (that do up at the front not that go over the head) maternity pads, lots of pants, food, water jug and cup, phone charger and a pillow. All in a suitcase that you can wheel. Good luck!