The refrigerators are small. A half gallon of milk would have to be stored on its side (potential for leakage) and would take up the entire shelf.
One way that helped us was to buy the "milk juiceboxes" at the grocery store to bring on our trip. They don't have to be stored refrigerated.
You can just put the ones that you want to have cold for the day in the fridge - which leaves you plenty of room for other things - cans of soda, little bottles of wine, spring water bottles, juiceboxes and whatever. You can squeeze the milk out of the box into your bowl of cereal.