I know that evidently many people use a knife to gather firewood and it really puzzles me. I use dead wood for fires, not green items which could require a tool. Simply gather the dead stuff and break to size, using your boot or a suitable rock (call it Neanderthal batoning). If you want to burn a large log, a fairly rare occurrence in my experience, simply feed an end into the fire and keep pushing it in as it burns.

The only situations where there was a dearth of dead wood was in heavily used campgrounds and in those situations gathering of live wood was prohibited.

I have frequently had to keep a fire going all night and I just haven't had a problem gathering all the dead wood I required - no knives required.