I had been thinking about posting a similar thread to this recently, because I despair of my species on a daily basis as I see the quantities of stuff discarded in public spaces. The most common items seem to be takeaway polystyrene, drinks cans - particularly those vile-looking energy drinks - and cigarette ends, the last of which I don't think has been mentioned here yet.
I did read something recently, I think in the Indie, saying the annual cost to local authorities to clear up what they do is approaching £1b. As someone who works for an LA, I know we've had our pips squeezed across central government funding, which accounts for most of our income, in the last five years. Whether this contributes to a decreased level of clean-up could be open to debate, but I shouldn't imagine it helps.
nb. I am not suggesting blame be apportioned to LAs or Westminster for litter.