Literally just the essentials.
With my first I went over board. Basically packed like I was going on vacation.
What's in my bag now (36wks with second)
-pair of sweats and pajamas
-loose tank tops
-2-3 outfits for baby (anticipate possible blowouts)
-baby socks + a pair of mittens
-tooth paste + tooth brush
The hospital I delivered at provided diapers and wipes + a kit that included a nose sucker, hair brush etc
Don't pack anything tight fitting. After birth you will want to be as comfortable as possible. Bring shirts that give easier access to breast feeding.
Don't pack a bunch. Just the essentials. You might even be like me with my first and basically wear the same thing for the two days you're in the hospital. Sometimes it's easier to be scrubby.
My list from when I was pregnant with my last (I did over pack but I ended up staying in the hospital for 4 days after)
robe/slippers (something comfy, you could be there over 48 hours)
flip flops (for shower)
cotton loose underwear
to go outfit (something you fit into around 20 weeks)
razors to shave armpits
*camera/extra batteries, charger, sd card, film etc.
money for vending machine
nursing bra/ sports bra
*check with your hospital before hand, some hospitals supply these things, some do not. Some also make you pay.
2 onesie outfits
blanket for carseat
Change of clothes
travel sized toiletries
you can bring extra pillows, blankets, linens etc. to be more comfortable.
You can pack your hospital bag as early as you want. I would not pack later than 32 weeks.