What to pack on a vacation to Texas?

We'll be going to San Antonio & then Houston. Some of the places we'll be visiting are the River Walk, Sea World, & Six Flags. We will also be shopping at one of the malls. I'm not quite sure about the amount of days, but you can estimate around 4-5. I'll have some down time at nights because our parents are going clubbing & to a concert, so nothing really dressy up is needed. Oh, & I'm 13. There will be about a 13 hour drive from our location as of present, & another 3 hour drive inbetween cities. Thank you for your assistance.