After having done this a couple of times, I learned what was most helpful for labor and delivery. There really isn't a whole lot you absolutely need. The hospital does provide you with many necessities like diapers, wipes, and blankets for baby as well as the big underwear, large pads, and cooling pads for mom. The hospital even provided us with a sound machine at night and body wash when I forgot mine. If you aren't sure what you are provided with, call your hospital beforehand so you aren't packing any unnecessary items.
Robe- That first shower after giving birth makes you feel like a new woman. I loved being able to put on my own clothes afterward. I packed two robes because I preferred to stay in a robe rather than any regular clothes. There is easy access for everything as far as the nurses needing to check you and for easily nursing baby. I didn't bother wearing a nursing tank or bra as I didn't see the point if I had a robe on but here are some of my favorite nursing bras in case that is something you want to have. (Or just pack to go home in)
Snacks- This may be my most essential item! You most likely won't know too far in advance what day/time you will be going to the hospital. Depending on the day or time of day, places may be closed or limited. Whether you're hungry in the middle of the night, waiting for a meal to be delivered, or your husband is hungry, I'm telling you- pack you all the snacks! You won't regret it.
Toiletries- Shampoo, conditioner, body wash, deodorant, toothbrush and toothpaste, dry shampoo, moisturizer, face wash, etc- Whatever toiletries make you feel nice and refreshed.
Blanket- After labor, I had really bad shivers. I was freezing cold and could not stop shaking. It was so nice to have a cozy blanket from home rather than just the thin sheets on my hospital bed.
Warm socks- Our hospital provided socks but I enjoyed having my own comfy warm socks- the hospital can get really cold.
Flip flops- These were a must-have to take a shower. I had cheap old navy flip-flops that I tossed after using.
Loose clothing- So important to have for when you leave the hospital. I personally did not want leggings or anything tight because you will be rocking a belly (still) and a huge diaper and pad.
Extra-long phone charger- I suggest the 10ft charger because outlets are often far from the bed.
Headband/hair ties/chapstick- Hospitals tend to be very dry so chapstick was crucial to have on hand. Also, can't forget those hair ties if you're like me and just want to get your hair out of your face and not bother styling it while in the hospital.
Velcro swaddle for baby- This is something I wish I had for my first two. The nurses do an amazing job swaddling newborns. I on the other hand had such a hard time getting the baby wrapped up nice and tight after each diaper change or feeding. Sometimes I would call the nurse back in just to swaddle the baby! But I didn't want to keep doing that throughout the night. I brought my own swaddle and was so glad I did. It was much easier to wrap her up after each feeding. Here is the one I brought.
Going home outfit for baby- I didn't pack any clothes for the hospital stay because I didn't see the point. (Unless you want something specifically for a cute announcement photo) Otherwise, I just packed two options of baby pajamas to bring her home in.