Rent a car and head to the Museum District. The Museum of Fine Arts is a good way to kill a few hours and admission is pretty cheap. Take a stroll around Hermann Park (right next to MFAH).

Pick a restaurant from this list and have a terrific meal. The list is a little out of date but it's still a solid collection. For instance, Downhouse is now open till 2am, not just 3pm. I'd also add Underbelly and Hay Merchant to it.

Just make sure to leave enough time to get back up to IAH, especially since it sounds like you'll be heading up during rush hour.