If you're an ambitious high school student who plans to pursue a double (or even triple) major, that's fine. Double majors are on the rise. However, you could help yourself out by not telling people about it. To understand why, let's think about the reasons why you might declare yourself a double major.
You're used to being involved in lots of varied activities, and you assume college will work the same way. This was the most common type of pre-double-major I saw as a high school teacher. If you're a top student taking AP classes in math, science, social studies, and English, then it makes sense that you might want to major in a number of those once you get into college. If you do really well both in the Science Fair and the Poetry Slam, then it makes sense that you won't limit yourself to either the arts or sciences when you get to college. You're used to doing everything, and you assume you'll keep doing everything. And the cool thing is that you really can keep doing everything once you get to college. But the thing is, you have limited time at college, and college is all about time management and making choices. So once you've committed to using up most of your credit hours--and most of your after-class hours--trying to pursue two degrees at the same time, you might find yourself unable to do other things you really like. You might find yourself spending so much time in the lab for a science degree you're not sure you'll use that you can't audition for a play or join a club. You might have to turn down a really interesting elective that piques your interest because it's at the same time as a required class that you can't put off. You may have to turn down a study abroad opportunity or internship because you're too booked up with your double major. Double majoring can, ironically, be really limiting. Consider waiting until you've explored the options at college before decided you're going to commit to two degrees.
You think it sounds impressive. I doubt that a whole lot of people want to double major for this reason alone, but it's likely a secondary reason for many who contemplate double majoring. It sounds like you've really got it together. People say "wow!" when you tell them that you're going to double major. But here's the secret: half those people who say "wow" are just being polite. A lot of them say "that's wonderful," but they're really thinking "why the hell would you want to do that?" I would tell students that saying you're going to double major is the long way to tell people you're undecided. Imagine a five year-old tells you she's going to be a police officer and an actor and a doctor. Your reaction to that is not very different from how a lot of college-educated people react when a high school student talks about her intended double major.
You want to have all the possibilities mapped out ahead of time. You recognize the importance of your few years at college and you want to maximize the potential of that time by having all the things mapped out before you go in. You know that you're really interested in nanotechnology, but that you don't want to give up your writing. You know that the arts are really important to a well-rounded person. And so you make an intricate plan that involves double majoring in Nanotechnology and Communications with a minor in Painting. That makes sense. But here's the thing: you're going to change your mind. College is all about exploring new ideas, learning what independence is about, and being exposed to new and different experiences. That's why 70% to 80% of students change their major at least once after they start college. You may know what you're good at, and you may know what you're interested in right now, but you've no idea where you're going to end up. And admitting that to yourself and leaving room for that is one of the most important things you can do for yourself before you get to college. Being comfortable with the idea that you don't know what's ahead is going to make whatever actually is ahead more rewarding and useful to you. You don't know the future, and that's okay. In fact, it's beautiful.
A double major will increase your marketability for jobs. No, it probably won't. There are some studies that show double majors earning an extra 4-5% over their peers right out of college, but those differences evaporate pretty quickly. I once got a tattoo from an artist who had a degree in architecture. I thought the extra knowledge base was really cool, and it gave us something to talk about while he was inking me. But would I actively seek out a tattoo artist who also had an architecture degree? Nope. Did he get to charge me extra for that architectural knowledge? Nope. Ask yourself: when choosing a heart doctor, how important is it to you that the doctor can also play violin? When eating at a restaurant, does the food taste better if the chef also studied history? Probably not. A banker who majored in Economics and Art History isn't necessarily a better banker--or a better art historian--than a banker who just majored in Economics and spent a lot of time in the art museum.
You have a lot of extra time and money, and you'd like to spend it on getting multiple degrees (most of you can skip this section). This is a wonderful problem to have, and I congratulate you on your commitment to academic study. But seriously, spend the time and money on extracurricular stuff, and then go back and get a Master's or two if you're still itching for more formal study. You can afford it. Pace yourself.
You're actually undecided about your major and you're afraid to admit that to yourself and others. This is really common, but it's going to be fine. Most people change their mind about majors, and most the adults I know say they still don't really know what they want to do with their lives. Being undecided means you're open to possibility, and that's a much stronger position going into college than pretending you've got it all figured out. Yes, you've got to declare a major and get a degree, but you don't have to know for sure what it is yet.
So, then what do you say? Whether you're planning on one, two, or three majors, use language that shows you understand how precarious that decision is. You'll sound a lot more wise and impressive than someone who goes through their (unrealistic) seven-point plan for the next six years. Instead of saying "I'm going to major in Economics," say "I'm really interested in Economics." Instead of saying "I'm going to double major in Economics and International Studies," say "I'm really interested in economics and international studies, and I want to see how I can connect them." Instead if saying "I'm undecided," say "I've got a lot of options where I'm going, and I want to see which I'm best suited for." Using this type of language--especially with yourself--is going to keep you open to the wonderful things ahead.
Please share this with someone who could benefit from hearing it. I'd love to hear your comments and questions.