A carry-on bag will meet the needs of most travelers on nearly every trip. Like the "$10 problem" rule, is it really worth the hassle to pack for every eventuality? Just pay the hotel to do your laundry. It appears expensive but is probably cheaper than checking an extra bag and definitely easier than carrying everything around.
Most people pack too much anyway. (Who needs a suit for one nice dinner during a two-week vacation?) Instead of a different outfit for every day, choose items with complementary colors that you can mix and match. Wear bulky shoes and coats on the plane. And always bring a swimsuit. You never know when you'll get an upgraded room with an outdoor hot tub!