Here's an easy one, get a steel bearing ball, a ferromagnet, and something made out of soft magnetizable metal. Put ball on magnet, touch ball with the soft metal, attempt to lift the soft metal off of the ball, watch in awe as the ball sticks to the soft metal instead due to that thing becoming a stronger magnet than the ferromagnet in the presence of a magnetic field. I did this in grade 8 and got an A+.
Or just go hit up a college, seriously they might have liquid nitrogen and a Dewar flask you could borrow to carry it in. From there there's a ridiculous amount of possibilities, just be careful not to generate liquid oxygen. That stuff kind of explodes.