Mardi Gras and the "other festivals" are two different animals. If you're talking about food that you can get at, say the Jazz Fest, there is nothing like that along the parade routes. If you're looking for cotton candy, peanuts, Polish sausages, etc., then you'll do O.K. But, food stands like at the festivals, good luck finding that. They would be very few and far between, if any. You might be able to find one of the nicer food trucks, but even they will be hard to find since the parade route is so long and spread out.
To: Golf Guy
You might want to try to find something a few blocks away from the parade route. Look along Poydras St. from St. Charles Ave. towards the River.