Did your school send you an orientation schedule? If so, look at it and see whether or not you will need any textbooks the first day (chances are you won't). If you are going to be given panels and presentations all day, sitting in the same room, wear layers so that you can be comfortable. If you are going to be up and moving around a fair amount (tour of the school, a lot of room changing, etc.), wear comfortable shoes.
You probably will not need your laptop, but you may want to bring it so that you can get it hooked up to your school's network, or to give you something to do if you get bored.
A few "just in case" things to bring--a copy of immunizations, an official transcript from undergrad, a copy of the orientation schedule, and a list of phone numbers for the school. (These will all fit into one folder, which you can easily fit into your book bag, and you should have a copy of these on hand anyway.)
Along with that bring a notebook, some pens/pencils, some cash (in case you want to get a drink/latte/food/etc.), your cell phone (which you'll probably want to put on vibrate or silence), your keys, and your wallet. Make sure you have your driver's license or other photo identification (because some schools require identification prior to making your school i.d.)
A lot of schools have you take a facebook picture the first day of orientation along with an ID picture, so wear something that will flatter your face (because those pictures will follow you through three whole years). Unless you wear something completely ridiculous, your teachers/administrators will not remember you, so don't worry so much about what they will think.