A flint rod and steel striker, and nothing else to go wrong.

Simpler than the magnesium block: no shaving step, just a hard scrape down the rod into your tinder. Faster once you have the technique, and it throws a serious shower of sparks.

The trade-off is that it needs better tinder. Sparks alone will catch dry grass, birch bark, cotton or a proper fire stick — they will not light damp wood the way a magnesium pile will.

Thousands of strikes per rod. Carry it as the backup to a lighter, because the lighter is what fails.