Might've been posted, but this is the BEST thing for battery life, by FAR.
When you know you're going to be in an area without service for an extended period of time, OR you know you won't be able to answer your phone for a period of time, put your phone in airplane mode.
It deactivates all wireless activities, messages, phone calls, wifi, everything...the phone remains on, however...it basically turns into a clock. You can still access all your files, just can't make any calls, browse the web or send and receive texts.
Went to sleep last night, put it in airplane mode...82% when I went to bed...82% when I woke up.