How do you figure that? If I buy one less Widget, that's one less Widget that needs to be restocked, one less Widget ordered from the factory, one less Widget added to the production requirements estimate, one less Widget's carbon footprint. Seems like simple math to me.
If I tell ten people about my strategy and they buy ten fewer Widgets, that's ten fewer Widgets' worth of carbon footprint.
If you factor in material mining, transportation, production, transportation, storage, transportation, and packaging trash, that's a lot of reduction.
Not only that, my life is simpler, I spend more time making meaning rather than consuming, and am overall happier.
Or... I can waste my time trying to affect the political system, which I will never move a nanometer with all my effort, or affecting the corporations, whom I will also not move a nanometer with all my life's effort, etc.