Online ordering systems for fast food places let you fully customize all the toppings on your hamburger. But what if you could do the same thing for drinks? E.g, you order a soda but substitute the high fructose corn syrup with real sugar or your preferred artificial sweetener.

Then when Coke changes their formula to v3, you can just order Coke v2. You could also get bootleg formulations of the soda via GitHub (or The Pirate Bay after DMCAs are sent) so that people can mix and match flavors.

https://en.wikipedia.org/wiki/OpenCola_(drink) does something like this, but it's hard to mix the chemicals directly due to their toxicity in pure form.