You should pack a 'change of underwear'. [=additional underwear that you can wear at another time]
He answered the door 'in his underwear'. [=while wearing only underwear]
(..) squeeze me gentIy Hey, mister... you got the time? As a matter of fact, I do, Cubbie! Look at that! Time to honk your nose and puII your underwear over your head. Come on! Step right up here, don't be shy! Nobody Iikes... a bashfuI Ieather head. Move it! (..)1994 The Mask