Rack - Multiple Devices in one RU

Many times we have a single rack unit that uses a bracket that holds two small devices such as firewalls or switches. Meaning two devices in one RU. This makes it difficult to locate in the Rack Documentation all of the customer equipment.

Example picture attached.

I really don't want to limited this to two items. Sometimes you have a shelf that has a modem, and other loose devices just sitting there.. hate it, but its true.