How can I keep my iPhone alive?

My iPhone broke recently, I dropped it & the sleep/wake button is stuck in the phone. This has caused serious problems like not being able to turn the phone back on after I turn it off and in order to keep my phone from slipping into an endless restarting loop, I had to turn off the auto sleep feature. This creates a problem, my screen in constantly on & lit up not to mention I cant use the sleep feature to lock and password protect my phone. So my battery does not last very long and I’m looking for ways to keep it going. I’m going on a school trip to new york & were going to be walking around in museums all day for 3 days. Now I can charge it at night but, should I even bring it during the day? How can I really make the battery last with the screen on? I just hope I don’t get lost & don’t have a phone to call my group