I didn't go to public school here (I did in IL and CO, during the latter I would sharpen my knife in class to fight boredom), so I can't comment for sure. All I can say is that my old boss' son was caught with a SAK and was suspended for 6 weeks. Best bet is either assume the worst and don't bring anything at all, no matter how small, or check your school's charter/ask the principle or School District Administrator. I agree that having even a keychain SAK is a great convenience, but I'd imagine being suspended or expelled is an even greater inconvenience.