Where Do We Begin?
Let me begin this post by saying you don't really need anything to do yoga - it can be done anywhere, at anytime, with only your body and your willingness to listen to it. As a Western society, we have really sold into the idea that we need material things to make us happy - we believe that having more will make us more complete. The reality of it is, yoga in and of itself can lead us to a level of self awareness in understanding that we already are complete.
That being said, I'm a big fan of stretchy pants and sticky mats. So, if you plan on practicing at a gym or studio, there are a few things that may give you a good head start.