Whatever it is, we'd be surprised (I think) at how many people DON'T do whatever it is we think is our past-time. Just looking at the suggestions in the poll and in the thread, speaking for my family, 2 of the 4 of us don't Facebook, Twitter or text (OK -- texting, but not for actual conversation). None of the 3 women in my family watch (or have interest in) any sports, and I am really only a basketball and football fan. None of us shop for things we don't need. My daughters are vegetarian and my wife is very close to vegetarian -- so cookouts are something I dream of but never actually have in my household. Since we live in a cordial, but not friendly, neighborhood -- we have no neighborhood cookouts and since we don't have family nearby, family cookouts don't happen either. I drink beer, but my wife doesn't, and my 20 year old isn't old enough to do so (in our presence), but according to her admissions, she's not a fan.
Anyway, my point -- with my obviously dull and out of touch family as case in point -- is that America's past-time is hard to nail down since We, The People are not so much a 'melting pot' as we are a collection of diverse and free individuals whose joys and interests are as diverse as American's themselves.