The importance of extracurricular activities is closely tied to the selectivity of the college or university in question. At the most sought-after schools (those where the acceptance rate is about 25% or lower), it’s common for many applicants to submit near-perfect grades in grueling classes along with near-perfect test scores. Thus, in order to make the required hair-splitting decisions, admission officials usually turn to other factors to see what stands out. And at the top of the “other factors” list will be extracurricular activities.
If you are applying to the most hyper-selective colleges, the activities you’ve named above will be viewed by the admission folks as “worthwhile” but probably not head-turning. At the Ivies and their ilk, Key Club presidents are a dime-a-dozen, and—believe it or not—so are the founders of charities and other non-profit endeavors. Admission officials often have a soft spot for Eagle Scouts (it sounds so wholesome!) although, at the super-selective places, this achievement certainly won’t be unique. Your science/engineering organization sounds the most atypical, so perhaps this is where you can put some emphasis in your applications, highlighting it either via an essay or in the “Additional Information” section.
At colleges where competition is most keen, a student’s background is often very important as well. Hailing from a city, state, or nation that is uncommon in the applicant pool will boost admission odds. An underrepresented-minority, first-generation-to-college, VIP, or legacy background will be a plus too, along with any unusual life circumstances (e.g., growing up in a homeless shelter or on a houseboat). Of course, having an admissions-enhancing background is beyond the applicant’s control, unless, perhaps, you can convince your parents to move from Boston to Burikina Faso or Benin in the summer before your senior year. 😉
Bottom line: The more selective your colleges, the more admission officials will look beyond the transcript and test scores when making final decisions and thus the more your extracurricular undertakings will “count.” So while, at many colleges, your “numbers” alone will determine your fate, at the very popular (and picky) places, your extras will definitely play a role in your outcomes … perhaps even a sizable role although not quite a starring one.