3 hour layover in Houston Texas?

I am flying from Florence Alabama to Portland to see family, alone, also I am 14.. Well my first layover is going to be 2 in a half hours in Houston airport.. What is there to do there? I have had a layover there before with family and it was huge, trains, mile walks, tons of people. Well how much money should I bring for food. I was thinking a money card with 40 on it to and from Oregon. What could I do and what would be the right amount of money??