First time runner - sunglasses or not?

Hi,

I started running 3 months ago and have a cross country half-marathon in 11 days.

And i cant decide on the use of glasses.. Never used them, but have seen people use them on sunny days..

Do you run with sunglasses when there is a clear sky and sun? This is a cross country run, so im not so sure the glasses will stay on my head :/