When we lived in France the first time (1959-1963) we brought with us a turquoise 1956 Mercury. We took that beast all over Europe with a rack that my dad made piled high with camping equipment.
Since the US military was in just about every country in Europe that wasn't behind the Iron Curtain, a very nice perk was gasoline at US military prices, instead of having to pay the what civilians did.
My dad would buy chits before a trip, each of which was good for 10 liters. They could only be redeemed at gas stations that displayed a US Quartermaster placard, so when it was getting to be about that time we all kept our eyes peeled for one.
Now my dad never really did learn much French. But he did know to say "quarante litres" (40 liters, or about 10 gallons). Then it was (apparently) my job to monitor the transaction.
I remember one time the gas station attendant wasn't paying attention and went past the quarante litres. But with the chits it was all (10 litres) or nothing. So my dad ended up having to pay the difference out of his pocket.
Boy, did I get in trouble!