I've met a lot of kids who have volunteered at hospitals. But I've only ever met one who worked as an emergency medical technician. She wrote her essay about her first night on the job when she did chest compressions in the back of a speeding ambulance on a 19 year-old motorcycle accident victim who had just gone into full cardiac arrest.
Volunteering at a hospital is a popular choice for high school kids. But I'll bet she was the only kid working for that ambulance company.
Lots of kids go to expensive summer programs at colleges. But I've only ever met one who spent his summers taking history classes at his local community colleges for $20 per unit. He got to know one of the professors, and she shared the reading assignments for her upper division course on George Washington. He didn't care whether any college would look favorably on it–that's not what it was about for him. He was just obsessed with history and wanted to know more.
Lots of kids play an instrument in the high school jazz band. But I've only ever met one who also played trumpet in a real mariachi band. He wasn't doing it to put it on his college applications–he just liked playing good music (and wearing the authentic mariachi outfit).
The problem with popular activities is that they're crowded. It's much harder to make an impact and stand out if lots of other students are doing exactly the same thing you are. And the truth is that if you really care about what you're doing, if you're really interested and you're not doing it just to put it on your college applications, the popular choices won't be appealing to you.
If you really want to help people, you probably won't be satisfied volunteering at a hospital doing exactly the same thing the other 30 student volunteers are doing. Why not work at an ambulance company? Or better yet, volunteer at a mobile health clinic that travels to the poorest parts of town. Or find a doctor who focuses on under-served populations and offer to help her for free.
If you really want to learn more about history, don't pay thousands of dollars to go to a famous college's summer program where lots of other students are just paying to play. Go after your knowledge and take a local class with only 12 students, one where you can really get to know the professor. Or read as many books as you can about the period that interests you. Or email a professor at a local college and ask if you can meet him during his office hours so he could recommend the best ways for you to learn more about the Civil War.
If you really love to play music, you probably won't be satisfied just playing in the jazz band. You'll find a mariachi band, or a dixieland band that plays at retirement homes, or a slot at a local coffee shop where you can play on Sundays.
The students who have the most rewarding experiences in their activities, who ultimately stand out from the crowd when they apply to college, are the students who care a lot more about following their interests then they do about following the crowd.