blogPostNextPrev.liquid

{% assign ordered_posts = page.parent.children | sort:'published_at' %}

{% for post in ordered_posts %}
{% if post.id == page.id %}
{% assign previous_post_number = forloop.index | minus:1 %}
{% assign next_post_number = forloop.index | plus:1 %}
{% endif %}
{% endfor %}

{% for post in ordered_posts %}
{% if forloop.index == previous_post_number %}
{% assign previous_post = post %}
{% elsif forloop.index == next_post_number %}
{% assign next_post = post %}
{% endif %}
{% endfor %}

Put the code above at the very top of your two blog post templates (on the first line, above all the other code). Those two templates are:
“pages_show_blog_post.html” for blog posts with the sidebar activated
“pages_show_blog_post_wide.html” for posts without the sidebar
You can then access any page variable for the previous post and the next post — see the full list of available variables here: http://nationbuilder.com/page_variables.
An example implementation is to add a pair of buttons on your page somewhere, which could each link to the previous and next posts (and optionally include the headline of each):

You want to wrap your buttons in those liquid {% if %} conditionals so you don’t get a ‘previous’ link on your oldest post, or a ‘next’ link on your newest post.