If you are going outside of the United States to a foreign country, it is always a good idea to make sure your vaccines are up to date. Keep in mind that not all countries have access to the healthcare that we have. Therefore, many of them still have diseases that aren't prevalent in North America. Examples include polio, mumps, measles, and other airborne viruses. By making sure you are fully vaccinated you can prevent many illnesses from invading your body and turning your vacation into extended hospital stay. Another caveat: make sure the drinking water is safe. And it would be a good idea to bring healthy snacks, such as granola bars or other easy to pack items that are also convenient to eat and don't require the usage of a microwave or refrigerator.
Don't leave your medicine at home or go with only a partial prescription thinking that you can get a refill. Chances are it won't be that easy, especially if you are out of the country. Talk to your doctor and pharmacist before you leave and adjust your prescription refills accordingly. Even if you are staying in the United States it is always good to have a back-up plan. You may also want to talk to your health insurance company about health insurance coverage for travelers. It can offer you extra options that you may need if you're going out of the country.
One of the best things you can to do ensure your health and safety is to some research on the internet about any current health epidemics in the areas that you'll be in. Also find out where the near by hospitals are. Communicate your itinerary to friends and loved ones and make sure your emergency contacts are clearly marked in your phone as well as with any paperwork you carry with you.