Upvote:1
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 & the breathing can flow unrestricted.
When sitting in public transport, sit upright, close your eyes & meditate. Completely let go of any self-consciousness that other people are watching you & know what you are doing. Relax & 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).
Upvote:2
To answer your question, yes one can meditate anytime anywhere. The following might be far reaching example, however, during Buddha's time Ven. Maha Kassapa was an expert in meditation. As a matter of fact, he was the only person Buddha compared himself to be equal in the ability to enter Jhana at any time any posture.