Caffeine has been defined as a naturally occurring drug just like THC. Cocoa is also another source of caffeine. I think there's a pretty accurate list of plants that produce caffeine around somewhere.... a quick google search isn't picking it up, but found some interesting fact sheets.
Most sodas contain caffeine, either naturally (contain kola beans or brewed from kola beans) or added (Mt. Dew, Barq's, etc.) In order of caffeine levels, highest is Mt. Dew (54mg per 12oz/355 mL can), then Dr. Pepper, Coke, Pepsi, and on down the line till you get some like 7 Up with no added caffeine.
Doritos, on the other hand... nasty things. We should all stop eating them... just can't. Taste so good... mmm, cool ranch. /drool