I don't understand the comment about mental events, and lack of instructions for being mindful of what the body is doing. It seems to me to be quite clear in the Suttas.
In the Body section of the Satipatthana Sutta http://www.accesstoinsight.org/tipitaka ... .than.html
we have detailed instructions for discerning exactly how one is breathing:
"Breathing in long, he discerns, 'I am breathing in long'; or breathing out long, he discerns, 'I am breathing out long.' Or breathing in short, he discerns, 'I am breathing in short'; or breathing out short, he discerns, 'I am breathing out short.'
So, one should be mindful of the nature of the breath (long and short seem to me to be just some of the things that could be noticed).
And it seems obvious to me that this extends on to the other instructions, where even less detail is given. Surely this passage is talking about the walking itself, not the mind states (since this is in the body section):
"Furthermore, when walking, the monk discerns, 'I am walking.' When standing, he discerns, 'I am standing.' When sitting, he discerns, 'I am sitting.' When lying down, he discerns, 'I am lying down.' Or however his body is disposed, that is how he discerns it.
And so on for eating, urinating, and so on.
And then the elements, including wind element (motion), of the body:
"Furthermore...just as a skilled butcher or his apprentice, having killed a cow, would sit at a crossroads cutting it up into pieces, the monk contemplates this very body — however it stands, however it is disposed — in terms of properties: 'In this body there is the earth property, the liquid property, the fire property, & the wind property.'
So one should notice hardness (earth), heat (fire), motion (wind) and cohesion (water) in the body.
"In this way he remains focused internally on the body in & of itself, or externally on the body in & of itself, or both internally & externally on the body in & of itself. Or he remains focused on the phenomenon of origination with regard to the body, on the phenomenon of passing away with regard to the body, or on the phenomenon of origination & passing away with regard to the body. Or his mindfulness that 'There is a body' is maintained to the extent of knowledge & remembrance. And he remains independent, unsustained by (not clinging to) anything in the world. This is how a monk remains focused on the body in & of itself.