In Japan they don't have public trash cans so if you eat a snack you just shove the wrapper in your pocket until you get home or wherever. You end up with a pocket filled with trash, ha
They don't have them because they were removed after the Tokyo Metro nerve gas attack in 1995 as a precaution against future terrorist attacks. It's a pretty common response to terror attacks, France did it after the 1995 GIA bombings and the UK did it after the 1993 Bishopgate bombing by the Provisional IRA.
Everyone knows a bomb can only explode if it's within a trash can. I'm glad Japan no longer has to worry about this critical issue.
I all seriousness though, by all accounts I've heard Japan is very clean. The lack of trash cans is not an excuse people use and things work fine without them.