Where to leave gospel tracts?

Every time you go to a gas station, leave a tract in the credit card slot at the pump. The next person will have to take it out to put his credit card in, and will appreciate having something to read while he's filling his gas tank.... Every time you go to the grocery store, discreetly go down the beer aisle, placing tracts in the top slot in beer cases.
(The Way of the Master training manual, p. 37-38)