The Real Thing

I have a book called The Big Book of Big Secrets by William Poundstone. It was a bargain book at Barnes and Noble. It has a section on cola. It turns out that cola flavor has nothing to do with cola nuts. It is a "fantasia flavor" meaning a new flavor the arises from a mixture of othe flavors such that the original flavors can't be identified. In cola, the flavors are vanilla, cinnamon, and citrus oil. The oil is bitter, so sugar is needed to tone it down.
The exact citrus oil varies, We have had Lemon Pepsi, so it seems likely that in Pepsi the oil is lemon. Lemon Coke has been sold, but it did not taste right. Now there is Lime Coke, and it is good.
There are vanilla colas, and a few normal non-name-brands that have a bit more vanilla.
Pepsi had a Holiday Spice Pepsi, with a bit of extra cinnamon, plus some other spices, I think.
I want to make my own sodas, but carbonation is not simple. I need a regulator and a tank of CO2. Or I could use yeast to do the job like in home brew beer. You just refrigetrate after 12 hours to stop the fermentation.
Another way to do it is dry ice, or solid CO2. It should be food grade dry ice.
Carbon has an atomic weight of 12, oxygen is 16. 12+16+16=44. One gram mole of CO2 is 44 grams. A gram mole of a gas has a volume of 22.4 Liters at STP, which means standard temperature and pressure, 20 degress C, 30 CM mercury barometric pressure. So 1/2 liter of CO2 gas is about 1 gram. Dry ice has a density of about 1.6 grams per cubic centimeter, so a piece of dry ice about 1/4 inch has enough gas for a standard size soda. (The volume of gas in soda is about equal to the volume of liquid. Water can hold a lot of CO2.) Put in the liquid, put in a small piece of dry ice, and close the lid. Agitate. Refrigerate. Do not point the lid at anyone, in case the pressure builds before the water can soak it up.