Once you decide to address the less cheese goal, you could try rationing your supply. Decide how many crackers and/or slices of cheese you are comfortable eating in a single serving (and be realistic or you won't stick to this), and bag them separately, to force a deliberate choice if and when you go and open up the second package of the day. If there are more slices in a package of american cheese than you want, and you know you will be too tempted, it is of course possible to immediately throw half of them away on your way home if nothing else works.

Or if you want to be bolder, just don't buy things that are conducive to incessant oversnacking. That way you exercise your willpower in the grocery store, not at home when you're hungry and your willpower is compromosed.