Don't give them access to anything to eat 12-24 hours before butchering. But do give them plenty of water to drink. This gives them time for their crops and hopefully most of their intestines to empty out.
If possible, put them in a smaller cage/pen the night before. That way it'll be easier to grab them one at a time for butchering and they won't be as stressed if you have to chase them around the pen. It will ease your stress too.
Buster's suggested list is pretty complete. It helps to have your work surface high, at least waist high, to keep your back from aching if you have to bend over all day.
One more thing to consider is if you plan to pluck your birds. If so, you'll need a container big enough to swoosh your birds around in to wet their skin (a big stock pot or 5-gallon bucket will do), a thermometer (a meat or candy therm. will work) and a source for hot water. Some folks keep hot water handy over a nearby camp stove, gas grill, or fire pit. Others keep water boiling on the stove indoors.
After your bird has bled out you'll need to swoosh him in scalding water, about 140 degrees for 30-60 seconds (
does that sound about right?). Hold him by his legs & agitate him up & down so the water reaches down to his skin. Test him after 30 seconds to see if a wing feather comes out easily. If so, he's ready to pluck.
Remember to let your birds "rest" in the refrigerator for 1-3 days before cooking or freezing to get their meat to relax & be tender for eating. Meanwhile, assemble your favorite chicken recipes...