I find that rolling them maximizes available space. Folding them doesn't keep them any neater or less wrinkled, so you might as well roll them so you can fit more in.

I tend to pack 1 pair of underwear for each day I am gone, plus 2 extras. Socks I can usually wear more than one day, so a new pair for half the days. The rest depends on what I am doing there. Business clothes for each day of biz, but also some casual stuff for the off hours.