Sonic Drive-In is a fast food joint that allows you to relive previous generations of fast food. There is no formal interior seating, as you are expected to pull up in your car, order your food, and then wait for one of the employees to rollerskate up to your car and deliver your order.
If you want to eat there, you're certainly able to. Otherwise, you can be on your way. There are also some sheltered outdoor tables to use in comfortable weather.