It's pretty common for people to throw away their lighters once they run out of fuel because a lighter without fuel is useless right?
The flint on a lighter is the same material as you've got in your standard fire starter. Ferrocerium.
When you strike a ferro rod, it gives a spark just like the one you get when your thumb spins the flint on a lighter.
So if your lighter dies, don't throw it out. You may need it to start a fire the old fashioned way. I'll show you how with this simple survival hack.
How To Make a Fire With an Empty Lighter
1. Scrape off plastic
Although not the most eco-friendly method, you can scrape plastic shavings off of your lighter and collect them into a pile.
2. Collect Flint Shavings
Move the striker back and forth so that you can collect the flammable ferro shavings. These will collect on top as you roll the striker.
3. Remove Top of Lighter
Now remove the top of your lighter so you can get a good spark when you strike the flint.
A cheap empty lighter still has your basic fire steel inside and in a pinch, you can still make a fire with one.