How to save battery life on my iPhone? - 1

So I'm going on a class field trip thing on Monday, and my phone tends to die really, really quickly. I have an iPhone 5 and I'm not sure if there's a place to charge my phone on the bus. It's a two and a half hour ride, we're leaving at 6:15 am and getting back at around 5 or 6 pm. Usually my phone just barely lasts for one school day. At the end of the school day it'll be at around 20-30%. I'm probably gonna need my phone to text my mom when we get back, so what are some tips on how to save battery life?

Turn it off until you are ready to text your mother.

Turn it off for most of your field trip.