I just brought our wheelie bin in (I forgot yesterday) & there were FOUR bags of it in the bottom 
In the alley behind our house (the bins are emptied at the end of it) we often find little presents hanging on branches, gateposts etc too.
Why don't these people take it home & put it in their own bins? Do they think they've done their bit by picking it up so they don't need to go that little bit further? 
I wish I could booby-trap the bin so the next person who opens it in the alley after it's been emptied gets a surprise of their own! 