Labor Day weekend brings the SW LA Zydeco Music Festival in Plaisance. Hard to beat that, but it is primarily focused on the music. If yer internal organs can take 12 hours of double-kick drum, and your feet can stand 1/2 a day of stellar bass grooves, then you might consider it. Plus you can wheel in your cooler full of whatever you like.
That same weekend brings the Shrimp and Petroleum Festival in Morgan City. It's got music, but that's just one of the many things to see and do. It's very laid back. The drive down Hwy 90 to Morgan City makes for a nice departure from the "prairie" festivals. And who doesn't like shrimp!?
Last year I missed Plaisance ---our flight into New orleans on Aug 31 was luckily cancelled!- (and we didn't become tourist-victims of katrina)... but I agree it is a beautiful day-long festival, and on the Monday following is the annual labor Day Boozoo fest in Lake Charles, a great lineup of music, food and family-oriented fun. Big Hat Fields has his big free bbq on the Sunday in between if I remember correctly.
But beware- it can be BLAZING HOT down there that time of year... often more than a Northerner can handle,
But I have great memories of sitting outside in 100+ degree heat with not a breeze anywhere, and humidity around 99%- sweat dripping from every pore while gnawing on a gigantic fried turkey wing (size of a baseball bat) and the grease drippings merging with the sweat.