Do you have one camera or two? I always like to have one wide to short tele on one body and a longer tele on the other. If you have something like a 28-80 or 28-105(or digital equivalent)that will help a lot. Another lens on standby or on the other body would be great such as a 70-200 or 70-300.
I did the ABF about 10 years ago and loved it. Have fun.
Try to be there for the balloon glow. As many balloons that will be there, you MAY be able to shoot at 400-640 ISO, particularly if you can get a spot where so many are close together, which should be no problem. Should be plenty bright. I doubt you'll need 800 ISO. If on a tripod, feel free to try 100 ISO.
The special shape balloon rodeo later that week is really cool too. Too bad you only have a day or two. Make the most of it and have several memory cards on hand, even if only shooting in jpeg.