How to create a component which has specific content on each page
So, you need admin to be able to add one or two piece of content to a specific page.

Let's say you have content type Product content type.
For the custom content you can create a new content type, let's say Banner. Consists of these fields:


Title
Description
Image
Link
Reference to Product


Then you can simply create a Views which lists all Banners which have a reference to the current Product in the page. (Using contextual filters and the referenced field)

All Admin needs to do is to creates a Banner and indicate the Product to be displayed in.

You can also check Prepoulate module, for letting admin create the Banner straight from the Product edit page.