- Keyboard.
- Mouse.
- Display.
- Speakers + subwoofer.
- USB headsets.
- Thunderbolt 3 dock.
- Several TB3 hubs (disconnected most of the time) with Ethernet, card readers, USB-A ports, HDMI outputs.
- 6TB external HDD.
- 3TB external HDD.
- 120GB / 250GB / 500GB external SSDs.
- 250GB external SSD, used exclusively by Mac’s Time Machine backup tool.
- 500GB SD card (plugged directly into my iMac Pro; it has a slot for it).
- USB 3.0 hub with on/off buttons for every slot.
- KVM switch that got only demoted to keyboard and mouse switch between my gaming PC and work laptop (the display is hooked to both but detects its active input and switches accordingly at the press of a single button).
- External CD / DVD / BD-R disc reader and writer.
…and I am still thinking of buying an external RAID enclosure, likely for 5x 16TB HDDs running in RAID 5 (so I’d have “only” 64TB and not 80). 
Also eyeing this world-first external 4-slot NVMe SSD enclosure – sold on eBay at the moment – and thinking of buying 4x Intel 660p SSDs at 2TB in RAID 0 config for 8TB of external SSD space in total.