It's better to accept it early on that you likely won't be "unique," and instead make smart strategic choices. The most important things above ECs are your grades and MCAT. If your stats are terrible, ECs won't help you. As for ECs, make sure thatyour volunteering has longevity. Thus, you want to make sure you start early in your college career, so that you have at least 200+ hours when you apply.
The best ECs are the ones that will rack up a lot of hours, yet still offer maximum flexibility for study time and free time, thus allowing you to get the best possible stats. If you want to try and score more uniqueness points, I would recommend piggy-backing a sporadic non-clinical volunteer experience on top of a weekly clinical volunteer experience. The clinical volunteering will get your foot in the door, while the non-clinical will provide interesting talking points for your PS and interviews. Remember, ADCOMs have seen just about anything and everything. Unless you're an astronaut, Fortune 500 CEO, a famous athlete, or something similar, then you won't be very unique. If you start a successful non-profit, you might be considred unique.
Oh, and make sure you mention hobbies too.
At the end of the day, very few applicants would have actually done these things had it not been for medical school admissions. I don't see why people on SDN try to make others feel guilty for box-checking. The end goal is medical school. That's the only thing that matters, not the journey. At the end of the day, you'll be sitting in the same seat as your fellow classmate. Whether you did six volunteer experiences or two, it's all the same. If you spent too much time trying to be "unique" and let your grades and MCAT slide to the point where you couldn't be admitted, well then sorry to say, but um... You failed! In that case, the whole "journey" everyone seems to care so much about may not only become meaningless, but can also ruin your life. I knew a few people whom this happened to, but I'm saving that for a future post. It's always better to be smart (by making good strategic choices) than unique.