T.F.
I always kept a stock at home, actually, I still do because it is just habit.
A mainstay was always markers, colored pencils, crayons, graph paper, extra notebooks, erasers, pencils, rulers, protractor, and pretty much you name it. I had a large bin in my pantry that was all school supplies.
Today, most of it has dwindled and my bin is not nearly as full but you can bet my junior in college daughter goes through it when she comes over for dinner weekly to see if there is anything she needs. :)
It was harder for me to keep the poster board and keep it in pristine condition. Most of the time, I ran to Staples for that.