ok i did some research and i think we wont go for the rental car
its over 300 now for the weekend and the car will be parked most of the time, thats not an option!

i found out that if u take the train from Rygge – Rakkestad its about 25 quid! (euro)
from there it should be easy enough to reach gatebil, or cheap with the taxi (think around 11km)

hopefully there is some kind of tesco or some shop in rakkestad