How do top consultants cope with long workdays (long hours traveling and working) and stress?

It starts with the mindset in which consultants come in expecting long hours and high pressure to perform. Having that mental preparation is key to endurance, which is why the travel/work-life balance (or lack thereof) is emphasized during the recruiting process.  This mindset then level sets people's expectations so nothing comes as a surprise on the job.

Now let's talk about how people cope with it. Everyone has different strategies, but I'll outline the ones I found most effective:

  • Drink water throughout the day. Bring your own water bottle or purchase one and commit to drinking 6-8 cups per day. Not only does your body need to stay hydrated to survive, but your mouth will get dry from talking so much with clients/team members and getting up to go to the bathroom every 1-2 hours is a good way to make sure you're moving around. 
  • Bring snacks with you to munch on. This sounds like what a mother may tell their 5-year old, but this has helped me push through some tough hours. You'll encounter days when you completely forget about breakfast and lunch and then your stomach is throwing a hissy fit by dinner. Your attitude sours by then as well, so do yourself a service and have a snack reserve with you at all times. I typically bring cliff bars, trail mix, or chocolate-covered blueberries.
  • Allocate 30 minutes daily for something completely unrelated to work. Seriously. For me, it's usually a short run. It was hard getting started (as with most things), but after that first run and the subsequent rejuvenation, I was hooked. On days where I'm too physically exhausted to run, I'll read a chapter from a fun book (currently on Dan Ariely's Predictably Irrational) or, of course, navigate to Quora.
  • Bond with your teammates. This sounds obvious (and it should be) but I can't emphasize this one enough. When you're traveling, your project team becomes your second family. It's important for you to look out for each other. You will become a source of emotional support for each other when stress levels increase. With tight deadlines, sometimes you'll also be absorbing each other's workstreams (even when it's beyond "your" duties) and going that extra mile to triple check the deliverable is ready. And lastly, having the mentality that you're with friends as opposed to straitlaced colleagues makes the overall consulting experience more enjoyable.

Is taking vitamin supplements helpful or quackery?

Vitamin and supplements have shown to extend telomeres and over a lifetime may add about 5 to 10 years to your life expectancy. Here is an overview of the more important vitamins and supplements with an explanation of how they work.Vitamins and supplements needed for heart attack and stroke prevention1. Vitamin K2 has emerged

How should you start a career in Machine Learning?

The Stanford machine learning on Coursera was designed to help a broad audience get started in machine learning. If you're familiar with basic programming (in any language), I'd recommend starting there. Many people have gotten jobs in machine learning just by completing that MOOC. There're other similar online courses that help; for example

Can eating healthy be fun?

YES IT CAN! I love fruit and vegetables. Even thought it may seem gross there are many ways to make fruits and vegetables taste good. Sometimes I like to make fruit smoothies. It can be fun to try different blends of fruit.