Here's the link to the official SAT webpage listing what you can and cannot bring.
Note that you can't bring your cell phone, smart phone, or anything that can connect to the Internet, send or receive messages, or play or record video or audio. Also, anything with an alarm is out. You can bring a drink and a little snack (think granola bar or something else that won't make a mess, smell bad, or get ruined if it's stuck in a corner or in your pocket)..
Also, don't forget your extra batteries and a CD player if you're taking a subject test that requires listening!
Author: John Linneball Who did you think? ;-)
I'm the proprietor and only tutor for this business; that's why I named it after me.