It's dark and you need to be able to see. It's fine-whip out your trusty Android phone and put the camera into a flashlight. Here's how to do it.
Honestly, this could not be simpler, it's just a toggle away on Android phones. First, pull down the notification shade. Then find the flashlight icon and tap it.
Left: Off; Right: On
Really, that's it! If you can not find the flashlight icon, you may click here to see the entire Quick Settings menu. At that point, you should see the flashlight.
Now that you've found the flashlight, however, let's go ahead and eliminate that second tap by moving the flashlight icon to the top of the Quick Settings panel.
On Samsung Galaxy phones, click the three dots in the upper right corner, then choose "Button Order." 
From there, drag and drop any icons into your preferred spot, making sure to move the flashlight icon closer to the front of the list. From that point forward, it'll be little more than a swipe-and-tap away.