see if the facility has a list of what to and what not-
Take an ipod or mp3 player download tunes on it from your phone or computer before you go- helped me a ton
List of important phone numbers
Cigs if you smoke, enough for 30 days
Books or magazines (middle of the road ones) they will give you tons of reading material, its good just to read a book or magazine
Bible- if that's your thing
Clothes/ personal items above as everyone has said.
Best of luck, look at it as a gift.