I have a solution for every problem.
I just had another cool idea for luxury vehicles. The car would come with a set of special insulated beverage cups with specially designed for the cup holder, where the base of the cup would naturally orient the cup the same direction every time (essentially, sippy side toward the back of the vehicle). The cup holder would be mechanized and linked to the accelerator and steering wheel, so when you take a turn, the cup holder would rotate the cup with the turn, and when you accelerate the holder would tip back. In this way, your cup would never slosh out. Braking should be a non issue due to the directional nature of a sipping lid. A more advanced version could even have pressure sensors to detect liquid movement as it sloshes and make micro adjustments to counter act and neutralize the sloshing motion.