When I was in high school and went to a Mormon church cokes were a big no no.
I know. I've seen that myself. Many Mormons don't drink caffeinated sodas (I avoid them myself) but there is no actual doctrinal prohibition on them. We try to avoid unhealthy things and caffeinated soft drinks aren't healthy at all.
The church forbids smoking or chewing tobacco, alcoholic drinks, coffee, tea, and drug abuse. That is viewed as a minimum standard all members are held to, several choose to go beyond that and not drink cola or other high caffeine drinks as well, but it is not forbidden by the church.