Importance of Posture in Meditation I'm curious to know: how important is posture during meditation? Could someone meditate on public transport, or while walking in different places? Is there a difference in the necessity of posture between a beginner and an advanced practitioner?
Posture is extremely important however sitting cross-legged is not important. What is important is having a naturally erect spine so the mind is alert &amp; the breathing can flow unrestricted. 

When sitting in public transport, sit upright, close your eyes &amp; meditate. Completely let go of any self-consciousness that other people are watching you &amp; know what you are doing. Relax &amp; enjoy. 

As for walking meditation, this is something monks do a lot. You should try to learn how to do walking meditation (but not in a busy or dangerous place, such as when crossing a busy street in the city).