A lot of it will depend on where you are too.
If you can easily get to an electronic surplus or wholesale type of shop, keeping large totes full of old cables / ends etc is a waste of space. Keeping one or two on hand might be OK but even then, are you really going to have them with you when you actually run into the service call where you needed them?
Not all TV mounts come with the same assortment of screws, so a small container or having them with all your other screws etc makes sense. You don't need to save the left overs from the last 10 installs though.
Having a spare amp / receiver / pair of speakers can make you look good when a customer blows theirs up. What you don't need are shelves full of equipment that are so old they no longer have any value or use.
Like mentioned above, keeping old CD players or DVD players would be a waste of space.