Making homemade soda pop is fun and easy. I've even been experimenting with variations on already existing flavors to make other unique flavors.
All you need to make your own soda pop is:

1 Empty 2 liter bottle with cap
1 cup of sugar
1/4 a teaspoon of bread yeast
1 tablespoon of cola/root beer/ ect.. flavoring

First it is easier to use a kitchen funnel to drop all of the ingredients in. First put in a cup of sugar. Next ad the 1/4 cup of yeast. With the yeast on top of the sugar it is a good idea to put the cap on the bottle and gently shake the bottle to mix the yeast with the sugar. Next add your flavoring into the bottle. Last add about half the bottle with cool tap water, put the cap on and shake all the sugar, yeast and water together. After everything is well mixed up fill the rest of the way with water leaving about 1/2 inch from the top full. Let sit for 3 or 4 days in a dark closet. Anything over 2 weeks risk explotion. The bottle should be very frim. place in the refregerator over night and its good to drink the next day.