How to keep hair from frizzing?

I get up early in the morning and flat iron my hair. I have thick, wavy hair. My hair is decently strait when I finish. I like in southern Texas and it's almost summer time. It insanely humid outside! My hair frizzes up mega bad. I'm meeting the guy I like tomorrow, but by the end of school, my hair is wavy again! I thinks it's because of the humidity. Any way I can keep it strait and keep it from frizzing up without products? I have this, Frizz Ease Secret Weapon Flawless Finishing Cream. It "intently camouflages imperfections, leaves dull dry hair shiny, soft and supple. Would this help any?