We do the same. when the Mega millions reaches over $100 million. But the cost is $1.00 and since we sell tickets it's really 95 cents. we have a sign that says win Millions with Superwash Purchase. We simply print up a dozen or so Quick pick tickets at a time.
A guy at the ICA show uses instant tickets. Payouts are small but frequent. That creates a lot of buz among customers.
Other times we give away a free Air freshener. Since it is a custom freshener which cost about 40 cents a piece, the customer has a constant reminder of where to get his car washed hanginfg from the mirror.
On hot summer days, you know the kind where your car is parked outside nand you get in and the temp is about the same as the sun's surface, we fill a cooler with can's of soft dring and ice, and offer a free cold dring with purchase.