WordPress themes generally allows you to have a single sidebar. But, sometimes it is necessary to showcase different elements on the sidebars for each posts or pages. It gives you more flexibility over the content and what you want to show to different visitors on your website.
The most popular WordPress plugin to add sidebars is “Custom Sidebars”.
1) Custom Sidebars WordPress Plugin allows to create your own custom sidebars & widgetized areas and also select which sidebars you want to use for each post or page.
With this plugin, you can create all the widgetized areas you need, custom sidebars, configure them adding widgets, and replace the default sidebars on the posts or pages you want easily without touching the code.
2) Another popular plugin you can try to add custom sidebars is Per Page Sidebars. This plugin also allows you to create and display custom sidebars for any post (or page) on your website.
3) If you want to add a post-type widget, then try Widget Entries plugin. With this plugin, you can upload images to be shown directly in the widgets and you can also use shortcodes inside your widget.
This plugin lets you to format your widget with the WordPress editor.