My wife and I have successfully done several 10-day to 2-week trips to Europe using carry-on luggage only. Typically I pack 2 pairs of trousers (plus the one I'm wearing) and 4-5 shirts (plus the one I'm wearing). I have travel socks that dry out overnight after they've been washed in the sink. I pack underwear for a fresh set daily - I don't wear an undershirt.