I'm from Norway. Zip code thing completely threw me off first time I was renting a car in the US. Drove up to the pump, whipped out my card and... what? Why on earth do they need to know my zip code?

Didn't know any zip codes offhand so ended up paying inside, which turned out I had to do in advance of course, another aha moment. Inside the cashier naturally asked how many gallons I wanted. I had no idea. Rental car was not one I'd ever driven before, and I hadn't looked in the manual for the size of the tank. I took some comfort that the cashier had no idea either. And so there I was trying to guess how many liters the car's tank might be, how much might be left and converting that into gallons.

Back outside with a conservative 4 gallons to pump, the guy behind in line kindly informed us of the zip code of the area we were in, for next time. Came in very handy.