rucksack for day trips, classes
boots/shoes you don't mind messing up (for heritage studies or similar)
For Day-to-Day Stuff
Bring everything you need for your bathroom including gels, soaps, toothbrushes, shaving gear et cetera.
In addition to this bring enough clothes to last you a week without smelling icky.
Other things you may want to bring include:
an alarm clock;
any music playing stuff;
your swankiest disco clothes;
snacks (don't worry; you can also buy snacks on-campus during the opening hours of the campus Spar
This is for die-hard traditionalists so I think I'll just link these to the appropriate pages and you can decide what you want to participate in:
There are Things you CANNOT Bring
I have no idea what they are; check the literature you get from CTYI for the most recently updated list.
Nunchuks are strictly forbidden, prevented me from unleashing my inner ninja at the Closing Ceremony but. Y'know. Whatevs.
No Microwaveable Popcorn, for obvious reasons
No Roleplaying stuff
And the obvious no weapons, alchohol, drugs, etc.