Yerba mate, black coffee, or espresso are preferred sources of caffeine.

“My primary objective early in the day is to get into a mode of being focused, yet alert so that I can get work done. I found that the best way for me to achieve that state is through fasting. So I don't eat anything until about 11:00 AM or 12:00 noon. I'm not absolutely religious about it. There are days when I'll have a few Brazil nuts or a spoonful or three of almond butter, for instance, but most days I'm not doing that. I'm just not eating anything. I'm drinking some caffeine caffeine source for me is yerba mate, guayusa tea. Those are my preferred sources I tend to avoid coffee these days.”