My students LOVE to volunteer to help in the classroom. That's what gave me the idea to create actual JOBS that students can sign up for. Students have a job in my class for two weeks. I have students in each class that have the jobs.
It helps ALOT when I have a substitute. Now my attendance gets taken, students know where to get materials and who to ask.
My school has a "success" reward system where we give initial cards for the them when they are caught doing something helpful, good or behaving. I give initials each week to students who have jobs in my class. That is not the only reason they do it! They love it and I have to promise them that everyone will get a chance to do something by the end of the year. This is my second year doing this and I never have a shortage of volunteers.