What’s the best way to handle cable management panels, blanking panels etc.?

Any non-IP based objects can be added as assets in device42. Few differences from a device object:

• Assets don't have unique name constraint. Actually, it doesn't have a name constraint at all. You can add one without assigning a name(not recommended).
• Assets don't count towards licensing.

Here is a quick video on how to quickly add such assets to the rack.