It seems to be that the logical place to have a context based and role based menu would be on the left side. That being the assumption, the question is how to go about it, what does it contain, why does it need to change, when should it change.

I have been looking at several widgets and custom field plugins. Some of these deserve a deeper look. We might even should take a deeper look at how we are implementing custom fields and our plugin so that we have an abstraction layer.

Layering for custom fields in plugin

Here are some plugin in options which seemed to be able to handle some of this complexity.

There are really three places that custom field need to be used: so this post is not just about a dynamic left side bar. It is about a dynamic left sidebar that is run off of values in custom fields in the main post. So this post is talking about approaching custom fields with the best strategy.

• Just Custom Fields for WordPress plugin: This plugin adds custom fields for standard and custom post types in WordPress. After installation you will see simple settings page which is self-explanatory to use.

  I found two Posts about this plugin to be really helpful: http://justcoded.com/just-labs/just-custom-fields-for-wordpress-plugin, and http://justcoded.com/implementation/wordpress-3-vs-drupal-cck/.

• One of the ideas for the left side bar is to have a listing of related content. Related content could be all the files which belong in a single audio package, or all the digital files belonging to a physical item.
  This is where Related Widgets Plugin For WordPress comes in. The Related Widgets plugin for WordPress introduces multi-use widgets that allow you to list related posts or pages. To use the plugin, browse Appearance / Widgets, insert a Related Widget where you want it to be, and configure it as appropriate. You can optionally filter the results by category or section.
• List Related Attachments: List Related Attachments is a sidebar widget that will display a list of filtered attachments related to the current post. This might be useful in one of two ways: listing associated content, depending on how we implement it. Or listing the photos on the right-hand sidebar.
• Custom Field Template: This plugin adds the default custom fields on the Write Post/Page.
• Custom Field List Widget: This plugin creates sidebar widgets with lists of the values of custom fields. The listed values can be (hyper-)linked in different ways. One possibility is to create a list of all values of a custom field, which will be groupped by their post (or page) and (hyper-)linked automatically to this post (or page). Another possibility is that you can create a list of all unique values of a custom field and specify links as you like (or not).
• Get Custom Field Values:
  Get Custom Field Values allows the admin to use widgets, shortcodes, and/or template tags to easily retrieve and display custom field values for posts or pages.
• Advanced Custom Fields:
  Advanced Custom Fields is the perfect solution for any wordpress website which needs more flexible data like other Content Management Systems.
• Easy Custom Fields:This is a set of extendable classes to allow easy handling of custom post fields. https://wordpress.org/extend/plugins/easy-custom-fields/
• Advanced Custom Field Widget: The Advanced Custom Field Widget is an extension of the Custom Field Widget by Scott Wallick, and displays values of custom field keys, allowing post- and page-specific meta sidebar content.
• Custom Post Template: Provides a drop-down to select different templates for posts from the post edit screen. The templates replace single.php for the specified post.https://wordpress.org/extend/plugins/custom-post-template/

WordPress Custom Fields, Part I: The Basics : http://perishablepress.com/press/2008/12/17/wordpress-custom-fields-tutorial/

Custom Post Type UI: Admin UI for creating custom post types and custom taxonomies in WordPress.
https://wordpress.org/extend/plugins/custom-post-type-ui/