You can use a lighter to light a gas grill.
You can use a long match or long neck butane lighter to light the grill when the igniter is not working.
The igniter basically just sparks the propane to ignite it.
To light the grill with a lighter or long match, turn the knob to high/light and then position the flame of the lighter or match near the burner and it should light.
If you have small matches you can use the match on a long wire to allow you to reach into the burner without burning yourself.
You can bend the wire around the match to hold it.
Then light the match and then hold it to the burner as you turn the gas on to the grill.
Turn the knob to the high/light setting and then hold the match to the burner and it should light.