Amazingly enough, there is a lot that one person can do. Looking at yourself as a member of a larger community where all of your actions effect everyone else in some way helps to make this more clear. Is it required that you tow the environmentalist line? I don't think so. Sometimes, I think that when people believe passionately about a subject or way of life, they tend to scoff at those who do not adhere to that same lifestyle to the letter. It may not be feasible for your family to switch to a vegan lifestyle or to buy all of your products according to fair trade or organic standards.
No matter what we as consumers are told, or what we choose to believe, our lifestyle in "developed" countries, directly contributes to the continued poverty of others, and to the diminishing resource crisis that we are now facing. If you are visiting this site, my suspicion is that you are already beginning to question some of the things that we have been led to believe throughout our lives. The truth is that might does not make right. And while it is true that we can sometimes become agents of change through voting in our democratic system, what is more true is that we can vote with our dollars.
So, if you can do just one of the things that you research, you can make a difference. Buy your tomatoes from a local farmer. Try to cut meat out of one or two meals per week. Install a low flow showerhead, or shower only every other day. You could try starting a small garden, or canning/preserving your own veggies, or those bought at the local market. Join freecycle.com and share your cast offs with someone else who may be able to use them, or look for items that someone else has that you can avoid buying new. Say hi to your neighbor, or to a stranger on the street. Or buy a pound of fair trade coffee, or another fair trade item, just to test it out. Any of those actions, and a multitude of others can and will make a difference in the lives of one or more people, and if thousands of others join us, a movement and a message to big business could result.