Print your boarding passes, lol! Sometimes it is pointless, as they will just reprint them when you get there and if you have to check bags you have to wait in line anyway, but depending on the airport, Airtran has a separate line in some for those who only need to check bags and already have boarding passes. Orlando had the separate (and way shorter) bag only line, Kansas City did not. But better to have them than not!
Also if you pay for your bags online ahead of time, print the receipt and take that. When I checked in ahead of time coming home and paid for the bags, it didn't show up in their computers, and they would have made me pay again if I hadn't had the receipt (and yes, the charge did go thru!).