Did you know you can use the LED camera flash on the back of the iPhone as a flashlight? It can be pretty handy in a pinch, and there are two easy ways to activate it.
From the Lock screen, hard press the flashlight button in the bottom left of the screen to toggle the light on and off.
Alternatively, open Control Center and use the flashlight button there. This technique gives you even more control – a regular tap toggles the light on and off, while a longer press allows you to define the brightness of the light on a sliding scale.