I'd say don't bring weed on a school trip. Some kids at my old school got expelled for it.

But, it you need to, hide it damn well or don't hide it at all. Damn well would be in a shampoo bottle, burried in re-sealed box of food, inside the lining for your boot, ect. Be creative. Not hiding it at all would be just in your pocket. Are they really gonna pat you down? I doubt it. They probably wouldn't feel it anyway inside a coat. Or put it in your gloves and put them on.