Excel-lent Idea
When I was in university we had a machine that gave you a little slip for the windshield to show you paid to park there, so I used Excel to make duplicates and put them in my windshield every morning without having to pay the $8/day to park. But that eventually came to bite me from behind.
I got caught after about six months when the machine was broken one day but I still had a slip on my dash.