I always pack a change of clothes, including socks and underpants, in my carryon. I've never had to actually use it, but if I were to forget to do that, that's when they'd lose my bags. I only ever lost bags before I started doing that.

If you bring toiletries in your carryon, make sure that they are under the 3 ounces or whatever their guidelines are. Also, don't forget that you can easily buy more toothpaste or whatever. I'm always forgetting that the place I'm going to has stores as well.