I think the combination of experiments and old food my eldest kept under her bed (and didn't tell me about) were likely biohazards. I'll note that about the petri dishes and ask the school to dispose of her science fair exhibit (though I bet they just toss stuff like that in the trash).

I found some places selling the original Scooby-Doo series - there are some boxed sets with all three seasons packaged in a Mystery Machine - I think I'm going with that one!