The lyrics of the song state:
"Once in khaki suits, gee we looked swell
Full of that yankee doodly dum
Half a million boots went sloggin' through hell
And I was the kid with the drum
Say, don't you remember, they called me Al
It was Al all the time
Why don't you remember, I'm your pal
Say buddy, can you spare a dime?"
These two paragraphs talk about how men went to war full of patriotism (yankee doodly), and the rest of the song mentions other many ways in which they served they country; only to be now, after all this is done, forgotten and neglected to the point of poverty, thus the asking for change. This song was framed in the 1930s, so the economy was in a big crisis.