There are a few things that I carry backups for. Fire starting is one of them. Spark light, ferro rod, matches, mini bic. I will have some water purification tablets in addition to my UV pen.

For most part, I make sure to maintain my gear in good shape, ensure that I have extra batteries, and things that are crucial are on my person and not my pack.
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"I reject your reality and substitute my own..." - Adam Savage / Mythbusters