I may finally be back, taking a similar trip soon. You'll be good if you're open with staff.

Comfortable clothes (several days worth)
Your own toiletries (toothbrush, toothpaste, hygiene, etc)
Smokes if you need them
Something to keep your mind busy (books and the like)

Pack like you would for a small vacation, save for anything that staff might perceive is dangerous.

You'll likely be given a short period of time to make a phone call each day.