Since all the cheapskate airlines charge for checked bags now me and my girl resorted to carry on only. On AA (we hate AA) you get one carry on and one floor bag free of charge.
What we do is pack all our clothes into vacuum sealed space saver bags like these and then put shoes and accessories anywhere around them and the outer pouches of the carry on. We then also bring a slightly larger shoulder bag which is a decent size duffel and place any extra shoes and toys in those. Using the vacuum bags you cut your clothing down to half the space. One thing we were worried about was them starting to open the vacuum bags to check them but so far so good and Ill be damned if I don't put up a stink until someone gets a janitor with a vacuum over to help me.