You've probably already left, but if not, think about taking:
change for phone
phone numbers
dressing gown & slippers for you
lots of snacks / breakfast bars
squash
reading material
MP3 player
pillow (maternity pillow if you have one)
towels
DS2 was in hospital for a week before xmas, and it's hard work, but I'm sure this will get you the answers you need very quickly.
Best wishes. Will be thinking of you and your DS.