The only actual food items I've had at Sonic are their grilled cheese and fries. Not the healthiest choice for me to make, but then again, there's not much healthy about Sonic.
Not much healthy, but there's a whole lot of tasty goin' on. I normally go for their desserts- mainly their shakes or ice cream cones. They're cheap and strangely delicious.
Plus it's fun to be able to pull up and have the server come out to your car like they did in the olden days.