There is unfortunately nothing I'd really consider roadfood-ish within walking distance of the stadium AND open on Sunday
All of the eats at the restaurant area just east of the stadium are very pricey and very corporate. Of those eateries, the one I hear the most good about (but still can't recommend) is the Moerlein Lager House http://www.moerleinlagerh...unch_Menu_June2012.pdf
If "short walk" includes up to a mile, I recommend Zola's for a very good pub-style burger: http://www.zolapubandgrill.com/Burger.html.
Most of the walk would be across a bridge from Covington's Mainstrasse area
Another long-ish walk but good eats and low prices would be Tacqueria Mercado, but they close for 3 hours on Sunday between 2 and 5. If you're going to a 1pm game, this should be fine, but 4pm, not so much :-) http://www.urbanspoon.com...ria-Mercado-Cincinnati
Many of the good places near downtown are closed on Sundays, even when the Bengals are playing. There are many crappy and/or expensive joints that are open, however.
post edited by TJ Jackson - 2012/10/03 12:34:28