Tool box(es)
Storage boxes of all kinds.
Therapy
Forgot to add an IR thermometer to the list above 
A spectrophotometer was the largest single purchase. But also recently a Brymen BM867s and precision current shunts to do accurate current and efficiency measurements, also these probes , they’re fucking amazing.
I still need to equip myself with proper reflowing tools. My hotplate is just a small copper plate heated by a soldering iron (but it’s temp controlled so quite nice actually), and an infrared reflow tool made with a car cigarette lighter .
I don’t want to think about how much I spent in components/PCBs for driver development 
More batteries than 99% of the population owns, and about a dozen chargers. Not to mention, giving up hundreds of hours of my time.