What household substances could be distilled
This is tricky. Besides water, nearly everything has some hazard associated with it.  And even water distillation involves high temperature (100C).  Be careful distilling alcohol: the azeotrope of distilled alcohol is 95% ethanol which is VERY flammable! Plus, technically speaking, distilling alcohol may be illegal where you live.

One thing you could do is distill water with dissolved substances, most likely table salt (NaCl).  This would help you test the principle that distillation is a technique for separating substances. In this case, distilling salt water should yield pure water. A more visual example would be brewed coffee or tea, which is a suspension and should separate into water and crud!

And after that, I'd be careful! For example, concentrating acetic acid (white vinegar) is dangerous, as concentrated acetic acid is both corrosive and has choking fumes.  I would not even consider trying something that is not food grade, given your requirements.