This simple card is a great classroom management tool.
On the first day of class, give every student a "Stuff Happens" card.
Explain to them that you understand that sometimes 'stuff' just happens. Then tell them that they can turn this card in to you if they are late to class/school, if they need a little more time to submit a paper/project, or any other excuse that you are willing to forgive.
They can only use it once, but let them know that if they never use it, the card can be traded in for 10 points on their final grade (or next test/project/paper/etc).