Where Did I Put My Coffee?
Japan doesn't usually have much litter. Schools teach kids to clean up after themselves (there are no Janitors; kids do the cleaning at the end of school) and the lesson usually sticks. If there are no trash cans around (and there often aren't) people will often just carry the trash with them until they find one.
Coffee cans, however, seem to be an exception to the rule. I find discarded cans everywhere. I guess the can is just too inconvenient to carry around with a person's other trash.