Hmmm the almighty PC. Probable cause is more of a color of law for the individual officer. One officer may see he has probable cause and another may not. As for what you can carry. I would guess no weapons means non what so ever IE knife,mace,baton,firearm,grenade,laws rocket or tow missile. However your school should have issued you a code of conduct which should include all items the school considers "A weapon" For instance a box cutter may not be in the print, nor a straight razor. Wearing a shirt is not probable cause even if the shirt were to say "I HAVE A BOMB!" Do to the Fact that on the back of the shirt it may say "Dont walk behind me"