Whichever material is used, the thinner it is and the more surface there is, and especially edges, the more easily it will ignite. With wood, this can be achieved by shaving slivers off it. One method to keep these together is to make a feather stick. The best wood from a tree is dead branches that haven't fallen to the ground yet.
If a fire is to be lit by sparks rather than matches, char cloth, punkwood, fungus or down are commonly used to catch the sparks. However, fungi should be selected with care as some release toxic fumes on combustion. Char cloth can be made by placing plant-based fabric (usually cotton) in a tin box into a campfire; like charcoal, it is the product of anhydrous pyrolysis. It is very fragile, and should usually be prepared only in small quantities.
Embers of burned paper, leaves and other sheetlike materials are easily carried off by air currents, where they can alight on other objects and ignite them. In outdoor campfires, paper can be wadded up to reduce this hazard; wadded paper also burns more quickly.
Magnesium is sold in stores in shaved or bar form. Shavings burn white-hot, are impossible to smother with carbon dioxide or sand, and can ignite even wet kindling. Solid bars are impossible to ignite under normal conditions (and difficult even with a welding torch), and are thus very safe to carry. Magnesium powder and shavings are pyrophoric (they oxidise rapidly when exposed to the air). It is dangerous to carry pre-shaved magnesium — at best, it loses potency, at worst, it can spontaneously ignite and is then nearly unquenchable. Magnesium bars are sometimes sold with a length of ferrocerium cast into one edge.