The Iowa Cafe fried chicken on Main Street is still some of the best I've had. This year, the BBQ baked beans are enhanced (made at the hotel restaurant) as it BBQ back in River City. Lots of new menu additions this year. You can ask for a 1-piece meal (not on the menu) and save money, too.
If you want to get ahead with food on a stick, the huge 1/4" bacon in the Iowa Farm area (huge pig) is tasty (but pricey) - but compared to the state fair, everything will seem cheap . You can also get other fried foods (fried Oreos, pickles, etc.) in the Alpine Village area just across from the Giant Sky Wheel. (Used to just be corn dogs before Main Street burnt down and was rebuilt several years back.)
If the water park is open, there is a full back back there for an adult beverage. The only special food there that isn't in the park is Dole Whip, I think.
If you drink non-domestic beer, and plan to have more than one drink all day, buy the refill mug. The mug (filled) + refill is cheaper than 2 beers.