I often wear a Du Rag (bought in the ethnic hair dep't of almost any drugstore or grocery) in summertime just to keep any wispies out of my ears. If you have fine hair that is prone to breakage, it's a good idea to wear something snugfitting and silky in between your hair and the helmet.

When it's wintertime and really nasty out, I wear a pair of opaque tights/nylons on my head. My braid goes down one of the legs, the panty goes over my head, and I wrap the spare leg around the base of my braid. This keeps grit from getting into my braid especially on rainy rides, and it shortens my braid up to a safer length.

When I do two braids, I just put one down each leg.