This might seem overly simple, but there are two things I always do when my hair is looking less than great and I need to look presentable quickly: a little, wispy bun and a bold lip. The bun takes care of any lank strands or flat roots and you instantly look more polished.
If you have some dry shampoo or hairspray on hand, even better. Bumble and Bumble’s Dryspun Finishing Spray is great for creating windblown volume. Spray with your product of choice, flip your head upside down, then create a ponytail. I remove the front portion of my hair (sort of where your bangs would be, then re-place them on top after I’ve already created the ponytail. This creates a bit of volume. Then twist the pony, and wrap in a circular motion until it becomes a bun. Secure with a few bobby pins. I think that this bun looks best when a bit wispy and loose, but if you want to look more polished, you could always pull it tighter.
Then, to distract the eye away from my locks, I create a diversion with a bright lip. This brings the focus somewhere else, and it always works–believe me. One time I was at work and my hair was sucking, so I threw on a matte, red lip and someone asked if I had been at an event. Works like a charm.