How will this work practically? Let's say we want to try this just for a month. Make a list of such companies and try not to spend our money with them. First of all, making this list itself isn't that simple, because of confusing and ever changing murky corporate structures (apps like buycott [1] can help here). In many industries, a handful of players control the entire market - just 3 or 4 companies control meat supply in the US, Monsanto controls a huge portion of seeds and so on. In the end we'll probably end up with a list of couple of dozen companies in our "bad list" and our options to shop (even the basic necessities) will be severely limited. Not saying it can't be done, it is just difficult to do it without some serious collective effort. It is definitely a good exercise to brainstorm ideas though, we gotta start somewhere.
http://buycott.com/