|Use your cellphone camera to look around|
objects without exposing yourself.
Flashlight. Makes a good flash light. Some even have a flash light App.
Memorization Tool. Camera still works and that could be handy for taking photos of things you need to remember. Like landmarks for navigating or things you are taking apart that you need to put back together.
Periscope. Camera makes a good periscope. You can use it for looking around corners with out sticking your head out.
Morale Booster. If it has music or games on it that could be a fantastic morale booster.
Compass. The compass on mine appears to work with out the Internet.
Fire starter. You can short out the battery to start a fire.
Stop Watch. Not sure what you would use this for but something may come up.
GPS Locators. The satellites that send out the GPS signals may still be working. So with a GPS App you can get your location.
Phone Calls. It may still work for a short time after the land lines go down. May not but you may need to contact family members or friends
Calculator. The calculator still works without the Internet and may be handy for the math impaired among us. Math is far more important than you may think for navigating, food rationing etc.
Secret Communications. You can password protect your phone and leave it for another person who knows your password to pick up. Then they can read or listen to your message. Could be handy.
If you are wondering how to keep your phone charged after the end of the world it may not be too hard. You can get a solar charger or charge it from a car battery. A car battery will charge it quite a few times before the car battery will need charging.