Waltzing Matilda is a sad song for sure, and about as anti-war as one might come across. Another anti-war song in that vein is Christmas in the Trenches by John McCutcheon. I started to learn it because it is a challenge song to learn a new run-down technique in which every 1 and 3 beat is another bass step lower, but the message of the song is so sad that I can't make my way through singing it without getting weepy and my voice catching.
Goodnight Irene is one of those songs that so many people have contributed new verses to it, that I can't say that I know what the original was like? Is that a Woody Guthrie song, or did he "collect" it from an older traditional? Anyway, a verse that I heard added by the same John McCutcheon as the paragraph above (no idea whether he wrote it) is:
Sometimes she sleeps in pajamas
Sometimes she sleeps in a gown.
The night Irene does the laundry,
she is the talk of the town.
Topdown liked that verse so well that he adds it whenever he sings that song now, too.