There is an interesting post over at thefword.org: food, fat and feminism about what constitutes activism.
I consider activism to be any action that serves to disrupt, oppose, or defy the established social or political status quo. The most effective and successful forms activism aren’t always the big think tank mega-conglomorganizations with big budgets and a paid full-time staff who can chase legislators around Washington all day throwing big wads of incentives their way; rather, its the thousands upon thousands of small personal choices individuals make every day that have the most far-reaching impact in producing changes in attitude and heart that truly make a difference. The personal is very much political.
From The (other) F Word
Here, here is all I can add!