I’m a huge fan of headbands. If you’re (me) having a bad hair day, you (well, I) can just shove your hair back and top with a headband and look vaguely normal (me again). Thin or wide, they cover a multitude of hair sin plus you can wear them with short and long styles, up or down so you don’t get much more versatile than this.
My current favourite is this Isaac Mizrahi triple hairband. It’s studded with rhinestones and at US$17 from Target, it’s an absolute bargain.