What exactly does "practical" mean to you? To me, it's just a manifestation of what Gramsci called "common sense" ("senso comune" in his Italian), which is itself part of what he called hegemony, or the mainstream intellectual/cultural ideas that justify the current regime. He argued that this common sense is the sort of popular philosophy that always surrounds us, which will always be uncritical of existing power, and that it's the job of leftists to reject capitalism's own notion of practicality because it cannot ever be practical to go up against the people who are deciding what is practical, by definition. Instead, we need to write our own version of practicality, because if we go around repeating the existing one, as you're doing now, then we're doing the work of entrenching it instead of opposing it.
So, for Gramsci, this feeling that you feel doesn't mean that it can't be done; it means that you're suggesting something that would threaten the people in charge, because they're the ones who get to define "practical." It means nothing more or less.
We learn and we organize. Speaking for myself, I started a worker cooperative and work in international human rights. I'm a member of many socialist organizations, some local and some international. I've joined more picket lines than I can count. I go to conferences, where I network with other socialists to start other projects and support each other. I've been part of local efforts against evictions, expanded police budgets, and so on, some of which actually won. It's not a mystery, but it is hard, and we have to keep showing up and doing it.
Also, if I may probe, I think that your dismissive comment ("it’s not enough to say give up plastic and make a peace sign"), which clearly implies that I'm not doing anything serious, is telling. I think that you're being defensive. Zizek (I think in "Sublime Object" but it could be in something else) notes that ideology, as he defines it, is something that we don't see in our day to day life, but being forced to see it is a painful process, and we often respond defensively to having it challenged. Your current worldview seems to take for granted that no one (at least, no one serious) is doing anything meaningful to change the status quo, or even has a plan for how to change it, but that's actually not true, so we end up in this strange situation where you think that saying the most superficial thing about the current state of the world is somehow explaining something to me.
If you're actually interested in that question that you asked, and not just using it rhetorically, I have approximately ten thousand reading suggestions for you. I've already mentioned Gramsci and Zizek, but they can be a bit esoteric. There are also very good and very practical theorists of revolutionary change, many of which were themselves practicing revolutionaries.