Interesting question! I'm enjoying reading the responses.

I've smelled much of what others have - including bacon, and other foods (and ITA that it's tempting to knock on doors!) all of the wonderful flora and fauna. And the occasional dead thing, including roadkill

But, what stuck out in my mind when reading the question when when DH and I would go mountain biking and I would pass what smelled like cilantro. DH is Eastern Indian and uses a lot of cilantro when he makes his curries (chicken or chick pea) which are so much better than anything in any Indian restaurant, so every time we would go mountain biking, I would crave his cooking. I think that's why he stopped going.