We (mum, dad & elder sister) all used to sing in the car.
I was interested to see that Schantieman and Bob Coltman both included
I've Got Sixpence

In this song we used to sing the lines:
"happy as the day when the airman gets his pay
rolling rolling rolling rolling home, blind drunk!"
though I think most people sing soldier rather than airman. Something to do with him being in the RAF I suppose.

We also sang:
The Quartermasters Store
Ilkley Moor baht tat
Billy Boy

Got me interested in singing from an early age...