I don’t just mean a wrench, unless thats it for you. I mean any tool you regularly use for work that you consider your most important. If you’re a software person name whatever digital tool you guys use. Whatever the career everyone uses tools I dont care if they are digital, verbal, physical or psychological. For me its honestly probably a flashlight, before I use any tools I’m always investigating with my flashlight or using a laser to trace lines.
I’m a machinist, so I use a huge variety of tools (setting fixturing, looking at prints and diagrams, fine measurements and gauges, CAD and CAM software, manual machine tools, etc.) The most important? Eye protection. I have excellent vision and would never jeopordize it to whatever extent possible and reasonable. I use safety glasses so often now for scenarios even outside of work, I forget to take them off when eating until halfway through a meal. Maybe I should be worried about the broccoli, though. You can never be too careful.
Stopper PPE is a fantastic answer.