For some reason it seems like we ALWAYS have something to throw away. Maybe it's an American thing, but London, unfortunately, has very few litter boxes or rubbish bins. At first it was really irritating and seemed sooo stupid, but turns out it's because terrorists were caught hiding bombs in rubbish bins. For safety reasons there are none in the underground and very few above ground. It is still irritating, but not so stupid anymore.
P.S. If you want to use the toilet, do it before you leave home or wet your pants :)