Think of it this way: med schools are concerned about non- clinical work experience, teaching experience, research experience, non-clinical volunteering, and clinical experience. The last category is actually divided further into shadowing, clinical work experience, and clinical volunteering. Most people don't have clinical work experience so shadowing and clinical volunteering are enough. Shadowing is basically following a doctor around and observing the practice of medicine. However, shadowing is not enough because it does not show meaningful interaction with patients. You have to do some long term (6+ months) of volunteer work in a clinical environment to show that you know what medicine is about, that you are a compassionate person, that you can interact with patients, and have taken the time to explore your career choice.
International trips are good for exposure (I guess), but they don't matter too much. I personally think it's too much money for a resume booster and med schools also see it that way. Why? Because they are too short in duration, involve minimal interaction with patient populations that you may be serving, and require the "volunteer" to pay for the "experience." This is known as volunTOURISM. Nevertheless, it is fine for exposure and good stories if you can afford it. That would fit into clinical or non-clinical volunteering based on what you actually end up doing.
Also, AMCAS requires you to list your activities, describe them, and categorize them into types. You can read more about that on the AMCAS guides in the AAMC's website.
Any questions?