Sometimes in the afternoon, or in the evening if a shoot goes long, the stuntman and self-described truth-seeker Reuben Langdon will make a cup of something called Bulletproof coffee. The drink — developed by the Silicon Valley millionaire and biohacker Dave Asprey — consists of black coffee, two tablespoons of butter, and two tablespoons of MCT oil, which Langdon describes as a high-grade coconut oil “that does good things for your brain.” He used to get raw butter, but has since switched...