Foreign countries are not the same as your own in terms of health dangers, and serious illness can afflict travelers who are not properly prepared.
It is of the utmost importance that you find out about the health risks present in the locations you are traveling to and get any appropriate vaccinations and medication.
In Australia, there are a number of standard vaccinations that the National Health and Medical Research Council recommends for all travelers:
You may or may not have already been vaccinated for some of these, so be sure to check before you travel.
Younger travelers are also at higher risk of certain conditions, and as such it is recommended that they look into being vaccinated against the following:
Be sure to check out health authority websites for countries you are visiting, to find out if there are any new health risks.