If a container holds at most 100ml of liquid, you can take it with you in your hand luggage on an airplane. I don’t know if they were there before this regulation, but I’ve recently noticed whole shelves in shops (e.g. Rossmann in Germany) dedicated to sub-100ml products: toothpastes, deodorants, shampoos, etc. Cute and useful.
Update 2010-10-05: Looks like the 100ml limit will be lifted by 2013, thanks to new detectors that will be deployed by then. I wonder what this will do to the burgeoning sales of bottled beverages at airports. [Source: Focus via Marianne Busch]