When I learned this song, I learned the railroad tracks verse a bit differently:

Kookaburra sits on the railroad track
Better get off or he'll be flat
Run, Kookaburra run, Kookaburra-(at this point slap both hands together to make a loud noise)
Well that's the end of that (Pretend to wipe hands clean/dust off hands)


I also learned the eating gumdrops verse as:

Kookaburra sits in the old gum tree
Eating all the gum drops he can see
Stop, Kookaburra stop, Kookaburra
Save some of those for me.