I pack all my chem lights in hard containers. Right now I'm using plastic tube mailers. They weight next to nothing and do a good job of protecting the chem lights. Never had one fail, and I've gone through a lot of them.

You also have to make sure they are not broken before you buy them. If you shake an unused light stick it makes a distinct rattle, which means the glass vial inside has not been broken. Once the glass vial has been broken, it makes a completely different sound.