Canadians who travel in the USA, will inevitably find themselves at a gas station, trying to pay with a Canadian credit card, only to be prompted to enter a USA zip code. Entering random numbers like 99999 or other combinations, all end in failure so we end up stomping over to the kiosk to declare that they do not have a zip code as we're are from Canaduh. The attendant - behind thick bullet proof glass - rolls their eyes at yet another fuelish Canuck, presses a couple of buttons, demands your credit card, and orders you to go fill up the tank and come back and pay.
However, one attendant in Washington says that we DO indeed have a zip code. Apparently we just have to take the three numbers that are in the postal code of the credit card billing address in the order that they appear, and then add two zeros onto the end in order to bypass the US zip code. So if your postal code is V8S 3Y1, you would enter: 83100 for the zip code and avoid all the hassles.
This theory has worked at Safeway gas stations in Washington and Montana. I'd love to hear if it's worked for you in other states and stations.