Always take a toothbrush and toothpaste, as tooth decay doesn't vacation just because you do, and always pack clean underwear in perfect condition.
“What would foreigners think of Americans,” she would tell me, “if you got in an accident, were unconscious, and some strange nurse would undress you, only to see your underwear was full of holes?”
If my mom were alive today she might add, for those using digital cameras while traveling, to not leave home without extra memory cards, a spare battery and a way to recharge it.
Here's my list of ten digital photography gear items, in my mom's tradition of, “Never leaving home without them!”