While I didn't find an extracurricular activity with the same kind of feel of academic decathlon in university, what I *did* find is that decathlon itself prepared me for college classes in general (much better than, say, my regular HS classes), so I exported my study skills relatively easily. And, if you have the time, try to take a varied courseload, so that you get the feel of that multi-subject curricula. Especially if you can take courses across subject area but with similar focus (e.g., if you like Europe, you can easily craft a minor or major out of studying a particular time period, and then you can augment that with classes in art, music, etc., of the time period. There are just *so* many classes -- really, the limit is your schedule and how many years you want to graduate in

)
It is pretty easy to find opportunities for speaking, whether in extracurricular clubs devoted to speaking, as peripheral duties to other clubs (everyone needs speakers, quite frankly), or in classes. And of course, interviewing and essays will be vital to the core curriculum (especially if you want to enter any professional clubs, try to get any kind of internships, etc.,)