It's more about being able to spin whatever you do than actually doing it. If you can emphasise the transferrable skills you've picked up and how they make you a suitable candidate, i don't think it's massively important how you gained them. If you do absolutely nothing but go to school and sit on your pc, it's going to be hard to find any way of evidencing this - but if you do at least some things with your life you've got a good chance. Having said that, if you're looking at 'just' making the grades, and it's a popular college, a few extra-cirricular activities may help.