This now seldom happens to us, because years ago I decided that we have enough money to buy duplicates of some things if we have enough money to travel as often as we do. So, we have pre-packed duplicates of all toiletries and basics in the "travel closet" (which is the upstairs hall closet where the luggage lives: I installed a pantry-type rack on the inside of the door, and all of this stuff is on it and pre-packed in pouches, where it can be grabbed and added to a suitcase. I'd leave it *in* the luggage, but the house is tiny and the luggage really has to be nested when not in use.) I have pouches marked "Theme parks" and pouches marked "Beach" and pouches marked "Wintertime" in addition to the regular toiletries bags for each of us.
Why did I do this, you ask? Dental floss. DH is very particular about dental floss and always worried it will be forgotten, and every time we traveled it seemed to proliferate, because he kept putting more in the suitcases "just in case I forgot it." On one 3-day trip I unpacked at our destination and found 13 reels of dental floss squirreled away in every single pocket and nook in the 2 bags we brought. It was utterly ridiculous, and right then I decided that life was too short not to pre-pack.