How to make my iPhone battery last whole day at Disneyland?

I'm going to Disneyland on saturday and would like to take pictures with my iPhone 4S. I need to make it last the whole day though, the ride over there from San Diego and the ride back. Anyone got tips? Anything you got to make it last.

Well, not sure if you'll like this answer since the product i have in mind has to be ordered and you'll have to wait for it to be delivered, but there's these backpacks with little solar panels that have enough power to charge phones and other devices… I found one on amazon.com and one of these days i'll be getting one…

It depends on how you use your iPhone 4s. I suggest don't use your Wi-Fi connection or any applications to help you last your battery the whole day.