Tinder

Tinder is the stuff that catches a spark. Everything else is just fuel waiting for permission.

What actually burns

birch bark    peels off, burns hot, works even damp
fatwood       pine soaked in resin, lights like a candle
dry grass     needs to be dead-dry and fluffed
feather stick  shavings you cut yourself, on purpose

The rule

Prepare twice the tinder you think you need. The fire will eat it faster than you can react.