How do I bend 8-gauge copper wire?
Wire that is 8 AWG is just a smidgen over 1/8" in diameter. Copper wire is also a soft metal that actually bends fairly easily. 

The trick to bending wire into a shape is to bend it around an object using the object as a mandrel. If your project is similar to producing something like the following then I think you can bend the wire simply using the bottle as the mandrel. For the tight turns at the neck of the bottle I would start by using a longer than needed length of wire at the broad part of the bottle and wrap down through the tighter and tighter turns at the neck. If you have an extra length to hold onto as you get into the tight turns it should be relatively easy to just form it around. After the bends are complete then cut off the excess foot or so of wire. In the example shown the maker actually formed a decorative ending on the wire.