Dude, I love campfire songs, and most of them you can play whilst you're FUBAR (F**ked Up Beyond All Recognition)! My idea of a campfire song is something that's easily played, easily recognizable and singable for most people, and something that everyone will sing out and have a good time with. My favorites:

Margaritaville - Jimmy Buffett
Country Roads - John Denver
All I Can Do is Write About It - Lynrd Skynrd (any Skynrd song actually: Tuesday's gone, Freebird, etc.)
The Drunken Sailor - Traditional
Knockin' on Heaven's Door - Dylan
Can't You See? - Marshall Tucker Band
Your So Bad - Tom Petty

Well, the list goes on and on, but this should get you started if you decide to go for it! They're mostly simple 3-chord songs.

Campfire Dave