Every year around Halloween I make $400-600 via adsense with http://trickortreattimes.com/ which lists trick or treat times for cities/towns. It felt like a good service to provide as you really have to hunt for the data. First year I did the aggregating myself, last year I added user submission which made it much more passive.
I make about $200-$300 per evening during Halloween. I go around to websites that list trick or treat times, I am short, dress like a ghost and collect candy for free than re-resell to convenience stores.
It's time for me to update it for another year!