Here is one recipe for Homemade Root Beer
5 gallons water
5 pounds sugar
5 pounds dry ice
1 bottle of root beer extract (McCormick's is 2oz and seems to be pretty popular)
Using a 5 gallon plastic container or some other safe container, pour in about 3 or 4 gallons of water, 5 pounds of sugar, and the bottle of extract. Stir this around to make sure the sugar is distributed. Add the dry and let bubble like mad while you enjoy the fog. I tipped my 5 gallon water container with the spout side up to it wouldn't freeze in the spout. After the bubbles slow down, add the rest of the water. That's it! Enjoy.
A couple of weeks ago, I was offered a variation that I doubted. Today, I made it, and it is GOOD! It's the exact same recipe but exchange the root beer extract with vanilla extract. Taste like Cream Soda! (Thanks Ted!!)
5 gallons water
5 pounds sugar
5 pounds dry ice
2oz of vanilla extract
So good!

