how to display all posts from multiple collections?

[salimbenfarhat]

Hello,
Please, how to display all posts from multiple collections?
Examples cookies and cakes collections. I want to display on one page, all collections posts.

[leebrian]

I'd like to see this in the example as well. Here's what I set up to include pages and all the collections (although I only wanted the pages with the specific page layout because I didn't want to search some other internal pages)...

<script>
window.store = {};
{% for page in site.pages %}
    {% if page.layout == "page" %}
        window.store["{{ page.url | slugify }}"]= {
            "title": "{{ page.title | xml_escape }}",
            "author": "{{ page.author | xml_escape }}",
            "category": "{{ page.category | xml_escape }}",
            "content": {{ page.content | strip_html | strip_newlines | jsonify }},
            "url": "{{ page.url | xml_escape }}"
        };
    {% endif %}
{% endfor %}

{% for collection in site.collections %}
    {% if site[collection.label].size > 0 %}
        {% for item in site[collection.label] %}
            window.store["{{ item.url | slugify }}"] = {
                "title": "{{ item.title | xml_escape }}",
                "author": "{{ item.author | xml_escape }}",
                "category": "{{ item.category | xml_escape }}",
                "content": {{ item.content | strip_html | strip_newlines | jsonify }},
                "url": "{{ item.url | xml_escape }}"
            };
        {% endfor %}
    {% endif %}
{% endfor %}
</script>