What is doctrine on ordinary daily posture?
In the Theravadan tradition, most of the rules governing posture don't come from the suttas, but rather the vinaya.  Specifically, they are found in the 75 sekhiyas.  The first 26 are almost all about posture.  

The reason for these practices is really no different than those related to appropriate posture during seated meditation.  And it has a similar set of challenges.  In the West, we often set up a dichotomy between the mind and body.  No such division exists within Buddhism.  Form is just another skandha.  Just because Buddhism meditates on the foulness of the body does not mean that it should be ignored or viewed as somehow less important.  The body is also a tool that can be used on the way to liberation.  A posture maintained ardently, with mindfulness, and clear comprehension will have a comparable impact on cognition.  It establishes alertness and vigor while a bodily posture that is not meticulously maintained falls into sloth, heedlessness, and dissipation.  An upright body is an upright mind.  They are not different things.