index.html

<div class="products">
    {exp:playa:parents field="product_collections" orderby="product_display_sort_order" sort="asc"}
    <div class="a_product">
        {if product_detail_image}
        <a href="{path=product}/{url_title}">
            <img class="product_detail_image" src={product_detail_image}"{path}_width310/{filename}.{extension}"{/product_detail_image} width="230px" border="0" alt="{title}" title="{title}" />
        </a>
        {if:else}
        <img src="/images/wg/picture_soon.jpg" width="230px" height="175px" />
        {/if}
        {if editors_pick}
        <div class="editors_pick">
            <img src="/images/wg/editors_pick.png" class="editors_pick" alt="editors pick" />
        </div> <!-- editors_pick -->
        {/if}
        <h3><a href="{path=product}/{url_title}">{title}</a></h3>
    </div> <!-- a_product -->
    {/exp:playa:parents}
</div>

product_display_sort_order is a Low Variables field type.