I was parked outside our village shop one day (back in E Lothian). Hot day, family in car in front (nice, new SUV) had an ice cream each-car, 4 windows came down, four wrappers thrown out. I picked them up, popped them back through the driver's side saying 'think you've dropped something'. I didn't stop for the barage of abuse I was bound to get!
Its not too bad where we are, there's noone here which helps! what we have is mostly wind driven but we do get the odd bit dropped in a passing place where someone's stopped-which I pick up. We have a lot of cyclists and walkers and am glad to say, doesn't seem to be a problem.