Avoid getting sick on a trip of a lifetime! I've suggested a few over-the-counter medications to bring with you.
My top 5:
These meds work. If you feel cold-like, flu-like, etc. symptoms, Airborne & Emergen-C are great to get YOU back. TUMS helps with the occasional upset stomach an unfamiliar meal can make you feel. I used either Imodium or Pepto-Bismol after each meal in a foreign country where sanitary regulations are not the same in the USA.
I hope this helps :)