Contact the school and ask them? That's where I'd start. And the youth center might have some resources! May works there, and she might be able to lead you guys in the right direction for placement testing. But they might do it through the school, too.
For supplies, backpack, paper, pens, pencils, pencil case holder is good for pens and pencils. Sometimes markers. Calculators, but the type might depend on your math class. Notebooks, at least one for each subject. Folders, also one for each subject at minimum. You can get binders and put loose leaf paper in them, one for each class. A lot of teachers will give a supply list for their classes at the beginning of the year, too.
Fun stuff like stuff you like to do or t think you'd like? Or fun stuff like generic look up "what's fun for kids my age" and do that?