Have you looked at MIT’s actual application? If not, go and look at it, because it might give you some insight into their process and values. You’ll see that there are a lot of ways on the application to talk about who you are and what your authentic interests are, including things like what you do purely for fun. MIT also has portfolio options where you can demonstrate actual things you’ve done.
The main thing is, do not try to mold yourself into some kind of “perfect MIT applicant.” Of course you need to pass an academic bar in order to be considered at all… but beyond that, MIT is not looking for “excellent sheep” who accumulate a pile of cookie-cutter accomplishments because they are told it would look good on an application.
“Applying Sideways,” as mentioned above, has great insight. Really, read that and absorb it. I also think it is helpful to read MIT’s values statement. (It’s actually a good idea to do this when applying to any university.)