T.S.
Just wanted to say that if you want to do a hot dish you can. A cooler not only keeps cold things cold it keeps hot things pretty hot as well, especially if it is covered in foil and wrapped in a few towels. Also many "hot" dishes can be served lukewarm or at room temperature, like mashed potatoes for example.
If you want to do a cold side that travels well and looks pretty I suggest a traditional pasta salad with an assortment of fall vegetables :)