Drinking soda pop has never been so scientific. U-Fizz is a contraption for putting carbonation into drinks that are not already carbonated. For $6.95, you get the necessary tube and caps to transfer bubbles from your mixture of baking soda and vinegar to a bottle of the drink you wish to carbonate. You could make this kit out of material laying around the house if you have it, but it would probably cost about as much to buy the parts separately as to buy the kit.
You can watch a Power Point presentation on how the gadget works, which I don't have the software for, or you can download a pdf file with almost unreadable instructions. But the process is not that difficult to figure out.
The question is, what do you want to carbonate? I took a look through the drinks I keep around for some ideas. Keep in mind here that I don't really like carbonated drinks; your opinions may vary.
Kool Ade. The perfect drink for this type of experiment. What you will achieve is something we used to call Nehi.
Sweet tea. That might not be a bad idea, especially with a little lemon.
Milk. Yuck, that just makes me sick to think about it.
Orange juice. I don't think this would be appetizing at all. I can tell orange juice is going bad when it starts to taste a bit carbonated. Anyhow, you wouldn't need the U-Fizz to put bubbles in orange juice, since it already contains acid. You just put a bit of baking soda right in the juice.
Grape juice. That would be good, kind of like a premium Nehi. Or even champagne! At least we can pretend.
Coffee. It wouldn't stay hot for the time needed, and using the U-Fizz with a hot drink would probably be dangerous anyway. We'll skip that.
I don't have any lemonade around right now, but that would be a good candidate for carbonation. I have some sassafras syrup for making hot tea. A more concentrated drink made with this syrup and some sugar might yield a root beer-like drink.
There are other methods for making your own fizzy soda pop, but the U-Fizz is probably the cheapest and simplest. And the kids might even learn something from the experience!