Sandwiches. Full on sandwiches cut into rectangles. In the bush on some shared ground. Neighbours and I still refer to it as the Sandwich Bush. No one knows who put them there and there's only 3 of us that share the ground.
Is it anywhere near a route that children take on their way to or from school?! Children have a remarkable ability to not eat perfectly nice packed lunches, get rid of the evidence in any one of a number of cunning ways, and then go home to complain that they're 'sooooo huuunnnngggrrrryyyyyyyyyyy!!!'
I always remember at school, when we had a bank of lockers at the back of the classroom, but there were a few more lockers than there were children, so the additional ones would get claimed and padlocked before long. Soon, there was quite an undeniable pong coming from the lockers, which intensified throughout several weeks.
At the end of the term, having checked all of the 'standard' allocated ones, the whiff was narrowed down to one locker - and the teacher demanded that the person who had put the padlock on this one unlock it forthwith (I don't recall if anybody did so or if they just had to bust it open).
It was completely full of a whole load of nasty, rank, bogging, manky sandwiches, all neatly stacked up. <boaky mcboakface>