I like boyshort-style underwear for after rides, to avoid seams in areas that might be chafed.

I keep a container of Wet-Ones in my bike bag for quick clean ups immediately after riding. They are great for removing road grime and grease, especially if it will be a while before you can hit the shower. They're also great for getting my hands clean after cleaning and lubing my chain. However I only use them on non-sensitive areas like arms, legs and hands.