I always hate to cool some warm soda by dumping a bunch of ice into it. It always dilutes it by melting the ice so fast and making it watery and less carbonated. This way will retain most of the fizziness and won't dilute it at all!
Step 1: You will need:
a Ziploc gallon Storage bag (Storage rather than Freezer, allows for more cold transfer)
a tray of ice cubes (the smaller cubes, the better)
1/4 cup of Kosher or other large salt crystals (I recommend only edible salts, not the kind you'd use on your driveway, in case of leakage) Regular table salt will do in a pinch...
1/4 cup water