I really enjoy an excellent pair of sunglasses. It's the one thing I insist on having with me each and every time I leave the house; there's nothing like a great pair to make you instantly feel (relatively) pulled-together, even if you're just running to the supermarket in pajama pants and an old sweatshirt. I'm also a semi-exhausted person generally, and sunglasses hide tired eyes, so there's that.
I'm also a little picky about the shape of my sunglasses; this is one place where I really enjoy keeping up with the trends. A couple of months ago I was into simple round frames; a few months before that it was the bigger, the better; right now what I like is a largeish round lens with a small wingtip on the outer edges (like the pair I've been wearing constantly these past couple of weeks).