Of course capital would like nothing better than a population that defines politics as the decision to shop or not to shop; business interests spent most of the last century trying to convince us to find meaning in such gestures. When we do that, capital wins, since unless you’ve got the capacity to grow your own food and ride a horse and buggy to work, you’ve obviously got to start shopping again at some point.
Impotent gestures like Buy-Nothing Day are symptoms of a left that prefers doing something to nothing, even if that something doesn’t even reach the level of an empty gesture. Fantasizing our power isn’t the same as building it, and we’re unlikely to build it by advertising our powerlessness in ephemeral pursuits.