I hike in shorts; have never liked long pants (in winter, I layer longjohns under the shorts.) I wear nylon shorts that have built-in nylon or polyester mesh briefs, which eliminates the need for separate underwear. For one or two nights, I just wear them without washing; for longer trips, I take a second pair of shorts.

Patagonia Baggies are my favorite. Others that work include REI's OXT shorts, and I've also used various "water sports" shorts (swimming suits.)