Frankly, a "Free Draw Day" sounds like bad news for the sub. I've found
that even at the HS level, many students, esp. at the basic level, can't
handle the freedom or lack of structure. I have several one- or two-day
lessons that require only pencil and paper, or simple tools for the 3D
class. These free the sub from having to keep track of more specialized
tools. The lessons are also good for emergencies--God forbid.
I try to arrange for particular subs who I know can handle all the
minutiae of an art class; once she's penciled me in, I tell the secretary
to call her. Depending on the class, if there aren't any thieves, I ask
a couple of trustworthy students to pass out the materials the class is
using for its regular assignment, and then check them in again. That
way, the class is still on track when I return.