Be prepared for a possible mixed bag. The weather can be very warm and abruptly turn cool and rainy. I'd take both shorts and long pants and at least one sweater or sweatshirt. WARNING!!! I love the Delta Queen and travel on her whenever possible but the rooms are small and hanging space limited except in the A rooms. Dresser drawer space is adequate. Plan on spending your time outside to truly savor river travel. You'll have a chance to play the calliope and fly a kite from the top deck, as well as participate in the usual games and activities. The homes in Natchez are lovely and do attend the Pageant if it's performed while you're there. It's impressive. You'll find the crew and staff friendly and accomodating. If you have any other questions I'll be glad to try to answer them.
Have a wonderful trip and do a review when you return.