Gas has low margins but is one of the main reasons you stop, coffee is cheap - incredibly as pointed out above - they provide a hot cup at a reasonable compared to a coffee shop cup it will still feel incredibly cheap. They can subsidize their promotions based on the amount of cups they sell outside of the promotion. Finally if you get a cup of coffee you may be more inclined to begin the breakfast ritual and you'll buy food too. Once you're out of your car and in their store, it is all mostly high margin items (except for cigarettes and lotto tickets).