Be prepared for it to be really hot and humid in Oklahoma City.
Light weight natural fibers will feel more comfortable in the heat.
Despite the heat you will still plenty of people wearing jeans, they are universally popular throughout America with all ages.
Casual or smart casual is acceptable even in smarter restaurants we would suggest you opt for smart casual to be sure to fit in.
Sunglasses and sunscreen (we love the Riemann P20 range for 10 hour protection) are vital.
Comfortable walking shoes are a must if you plan on seeing the sites that the city has to offer, (we love Hotter shoes, for total comfort and they look great too).