I know when my kids have gone on school sanctioned overnight trips, there is a parent and student meeting regarding behavior which will not be tolerated.
PArent will be called to retrieve their child. Kid signs it parent signs it.
Are the TWO deal breakers. If caught you are done/suspended/loss of all activities including sports.

Kids know it, they sign the notice they were fully aware of consequences.
If said kids knowingly break the rules, some perhaps already 18, and some close to it, what do you expect?

How can you blame a coach for what the kids did. Nobody put weed in their bags, nobody forced them to do this. They chose to do this.

Now they have to live with the consequences.