Next to losing your luggage, there aren't many things sadder than opening your suitcase after a long trip to find that everything -- from your underwear to your nice suit -- is drenched in blue shampoo. That's why the most important principle of Packing Toiletries 101 is sealage.
First, close containers tightly. Yes, we know that sounds obvious, but it's important nonetheless. As a backup, get sturdy plastic zip-top bags to hold all possible leakers -- shampoo, conditioner, lotions and other liquid products.
And what about those pesky pump bottles? One trick is to lodge a piece of cardboard under the lip and tape it in place.