Give class pets food and water and make sure their cage is clean. Janitors often don't take care of class pets, so make sure hamsters, rabbits or other pets have everything they need before leaving class. The kids can certainly help with this process a few minutes before school ends.
Ask the children in the class to wipe down their desks. Give everyone Clorox wipes or towels to clean off the top of their desks.
Throw away trash or papers on the floor so the trash cans are ready for the janitor to pick up.
Turn off computers and any other media devices in the room.
Place chairs in the proper places and make sweep the room to get rid of excess debris. Turn off the lights and lock up the classroom after all the students have left.