My response to kids who didn't supplies (pencils or whatever) was a simple,
"Oh, that's too bad. Tomorrow you'll remember and get to do the activity
with us." This seemed to teach responsible behavior and after awhile the
kids realized I wouldn't provide the items they were responsible for
bringing. This was for elementary kids; ages K - grade 6.
I used a modified version for kids who broke minor rules. "You know, I'll
be happy to let you be start painting as soon as you show me that you are
ready to listen to instructions."
Try it. It takes a little patience, but the rewards are tremendous.