An expandable tank bag would do the trick. You don't have a buddy there local you could borrow one from?
Otherwise, pack one backpack lightly, underwear, socks, t shirts toothbrushes, comb and just make do with what you have. Pack a pair of gym shorts or something to sleep in and you can wear them while you wash everything you wore on the way down, (either at your hosts, or at the motel).
Of course, your friend'll have to wear the backpack.