If you can find it get a copy of
The Long Trail
by John Brophy & Eric Partridge.

Also search the forum for Brophy as I've occasionaly posted quotes from this book on various WWI threads. (I can't get a response from the search today or I'd post you a link.)
For what it's worth my WWI songs are here, here & here. Mainly gathered from Oh What a Lovely War and The Long Trail.

AndyG