Jessica Zafra suggests giving plastic bags back to the establishments that gave them to us in the hope that they reuse them. I say (well, she does, too) it's better if we just refuse them unless absolutely necessary.
I understand needing huge bags for groceries or for a number of tiny things, but a small plastic bag to place a bottle of, say, alcohol is just a waste of plastic. For those purchases I just tell the cashier to give me the bottle and the receipt. "Huwag mo nang isupot" is a solution to too much plastic clogging the landfills.
Some stores are trying to implement solutions but they're missing the point. SM sells reusable canvas bags for groceries but they're hardly enough to contain all the groceries I buy (I do mine weekly). And instead of being progressive and allowing a shopper to bring any bag, SM insists on using the canvas bags they sell.
It's faux environmentalism at its tackiest on par with their faux moral stance of not allowing R-rated films in their cinemas.
Besides, I reuse those huge grocery bags. They're big and yellow and perfect for lining trash cans. What I find wasteful are National Book Store's handle-less bags that they heat seal (presumably to keep pencils from slipping out), which doubles the waste since it renders the plastic useless.
As with any environmental advocacy, what's needed is a change in mindset. We have to start thinking in terms of what we can reuse and what will be wasted instead of what we think we need or worse, what the stores insist we do.