My mom went back to college in her mid-thirties. In one class, she always had someone asking her for a pencil/pen/notebook paper. For a while she kept some cheapo pens and a legal pad in her bag for just these cases, until the instructor pulled her aside and let her know that even though itwas great that she was helping out the other, younger, students- a full TEN PERCENT of their grade depended on coming prepared to class. This was a business class, and being unprepared for a business meeting/interview/job hurt you in the real world, the instructor was trying to show that. She wanted the students to have to go to her if they were unprepared, so she would know. Granted, if it were a case of pens/pencils breaking, she would not count it against you.
I would ask the instructor of your art class if it is OK to lend someone a supply, if you plan on doing it any more, or if being unprepared could hurt their grade.