Demonstrate the "lesser known applications of the flute" - use it as a broom handle, a zimmer-frame, a toothbrush, a gong beater etc...

Seriously - I don't know much about flutes specifically... But I do know that 30 mins is not long for something like this... Personally, I'd be tempted to make a comparison of styles (as somebody else suggested) to show how versatile and useful the flute is... Show short pieces of baroque, classical/romantic, modern, jazz, pop/rock and latin styles, and talk BRIEFLY about how the flute fits into each genre and the variations in technique and style needed to play each one...
(And if anyone tells you that the flute can never fit into rock music, cite Jethro Tull...!)