Crowds are heavy. If you got the tickets out to the causeway, be sure and bring a chair. They only allow the collapsable chairs. We also brought a backpack filled with water and snacks. Since the wait on the causeway can be somewhat long, we also brought the kids Nintendo DSs. They allow you to bring in all of the above it's just that you have to go through security and let them see everything.
If you will be at the KSC for the launch, you can amuse yourself with the exhibits there; however, they will be crowded. Many people also brought their own chairs for here as well.
We've been to two launches and were lucky that neither was postponed.
Have fun.