You felt guilty spending it, because if you find no owner and there is no identification with it then you can keep it.

So good poem, but why would you have to give a hundred dollars away, and why would nobody take it?

"It all" refers to the campfire or everything surrounding the campfire or something else that has not been mentioned or alluded to in the poem? Burning a campfire appears redundant and I am unsure who wouldn't take $100.