I know I can re-share the post to my stream, but how do I point a non Google+ user to a publicly shared post?
The down-pointing arrow in the upper right of any post offers a menu (see below).
"Link to this post" is the direct link to the post.
At the top of the post there will be a timestamp between the name of the Google+ user and sharing range.
Click on that and you'll get a page for that post alone.
That link is what you can share with other users not on Google+.