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.