Having brought up the subject of ladies' undergarments: I definitely can't do commando. I suspect that most women can't. I have tried all-cotton, nylon with cotton crotch (forget that, especially in hot weather) and the very pricey but very comfortable Ex-Officio briefs, made of synthetic fabric but in well-ventilated mesh. I now use the latter exclusively because they are the most comfortable and best-ventilated, especially in hot weather. I unfortunately am subject to the ailment euphemistically known in TV commercials as "overactive bladder" so need to wear pads. There are actually a couple of good things about that--first, it eliminates the need to carry anything in the first-aid kit as compresses for severe bleeding (in fact, my mountaineering first-aid course instructor recommended sanitary pads for this purpose). Second, I don't need to take a change of undergarments. The bad thing is having to get up several times at night. I've discovered that I'm actually better off not to restrict fluids at bedtime--restricting fluids makes the ailment worse. And no, I won't take the highly-advertised medication--one of its side effects is possible dehydration during prolonged exercise.

I have read that both NOLS and the BPL lightweight backpacking courses recommend cotton briefs for women and taking at least two pair.