I'm a pretty simple person when it comes to everyday work makeup. Usually I only have 5 minutes, if any at all. But if I had to just pick one, it would be my eyeliner and lip balm.
Lorac Pro Eyeliner in Black
This eyeliner is unique in that the brush has the look and feel of a Copic marker (think soft brush marker). Anyhow, I fell in love with it's precision and ease of use. This makes doing any cat eye so easy and so fast. This eyeliner doesn't really fade on me, unless I'm swimming at the beach. (Then I have another eyeliner for that.) It lasts all throughout my shift without giving me raccoon eyes. (I used to have major problems with these with any pencil eyeliner.)