I can create a generic object to keep track of my items, called "Item".
This has a name, description, and images.
When I have a specific item type, like a usb cable, I want to have fields for it's attributes, so I can list and compare my cables.
Drupal content types are entity bundles. A bundle is a collection of fields on an entity type. Node is the entity type, and Page and Articles are bundles.
In order to have a cable inventory item, I need a way to have another bundle of fields on this one.
Here is a new project that can handle this type of thing: https://www.drupal.org/project/field_bundle. See also https://www.drupal.org/project/storage
In the past, I have used ECK (retrograde.bike), but it always feels like it should be done as custom code as the UI is not streamlined for what you can build with it.
There are now Entity Bundle Classes in Drupal: https://www.drupal.org/node/3191609