Ditto everything CF said about needing them and buying cheap ones at Target.
I splurged and bought a $20 pair last year at Cabelas, wore them twice I think, then I accidently threw them on the ground and stepped on them as I was walking into a store (sunglasses indoors ais a major peeve of mine).
I bought a pair of Fossils with one of LJs rewards cards - they look just like cop glasses.