Data don’t go through when you are in crowded areas, calls don’t go through. The best is to send texts. They always go through even with a tiny little signal.
If you have an iPhone, make sure to switch to send texts instead of IM (IM means data).
Go to Settings > Messages and turn the IM option off.
Don’t forget you have a flashlight on your iPhone available straight from the home screen. I have an extra flashlight from Surefire.
Have a snack in your bag (jerky, bar, …), something that has a long due date. I go for the Healthy Warrior energy bar.
Bring a bottle of water with you. I carry every day my Klean Kanteen (dishwasher safe).
I wear my survival bracelet, as you never know. Having a rope can be useful to close a door, tie a bad guy down … You never know. I wear my Survival Strap.
6. Extra battery
Add battery life to you smartphone.
Don’t panic, stay close to exits to be out as fast as possible if anything happens.
Don’t forget to carry your ID with you! Mine is protected by my Trayvax wallet.
I hope those advises won’t be helpful for you because you won’t face emergency situation.
Stay calm and safe!