As far as the soda thing goes, I’m fairly certain that if it does contribute to strings rusting, it’s not because “the sugar in the soda comes through the oils in your skin”, but it could be a combination of other factors.
The main cause of excessively rusting strings could just be the moisture in your sweat. If you sweat quite a bit, perhaps you’re getting nervous during performances, that can contribute to string rust.
Another factor is the amount of salt in your sweat. If your salt intake is high (odds are, it is), the salt in your sweat will make it more corrosive. Soda contains salt, and is not as effective in countering salt in your body as just plain water, which might be one origin of the myth.
If it’s bad, wash your hands and dry them before you play, wiping down the strings afterwards may help, along with other general healthy habits.