My father worked as a high school janitor. At the end of each school year, students threw away notebooks, paper, pens, gym clothes, and even shoes. Dad would bring home these items for the four of us kids to use.
One year, we had enough notebook paper to last five months, a supply of pens that lasted through the school year, and enough notebooks for all of us to have at least three each. We also had gym clothes and shoes to outfit us for the year.
Get friendly with school and university janitors then enlist their help. The end of the school year is a great time to pick up tossed but otherwise usable items. Debora