How to extend battery life on iPhone?

Hi, in a week I'm going to a concert that's about 2 hours away. During the ride there I won't be using my phone (to save battery) however my phone tends to lose a lot of battery even when I'm not using it. What is the best way to save battery while not using your phone? I have an iPhone 4 with iOS 7

Turn off auto brightness and keep it low or get a extended battery case

Put it on airplane mode, lower the brightness, also don't watch too many videos or browse the web. Get a black or dark background (Wallpaper) that does not eat battery. These are basics.