The car rental office is very easy to find, just a 300-meter walk to the left after exiting the airport. The paperwork is simple with no insurance upsells. We booked a Polo but received a very new Citroën C3. The trunk is spacious enough for two large suitcases and one small suitcase. The tank wasn't full, and you don't need to return it full either. Zakynthos isn't very big, so unless you're driving around the island every day, you won't use much fuel.