Necessities. Generally speaking, you may bring whatever you think you may need for the duration of your stay at the hospital. Basics like: clothing/sleepwear; toothbrush and toothpaste; hair and makeup products; etc. Your cellphone, laptop computer and reading materials are good things to bring as well. Insurance card and identification, admission papers and any prenatal records are important as well.
Positive atmosphere. It is nice to pack items that optimize your birth experience--lavender oil or other essential oils, soft lights, music that is meaningful/motivating (ipod and speakers). After the birth, it is nice to have some of your favorite toiletries and a comfy robe. I also recommend bringing your breast feeding pillow, since you'll be starting to breastfeed while in the hospital.