Whilst you could have anything you'd have at home, bear in mind that there will be a minimum of basic kitchen equipment, and a caravan oven is the most inefficient gadget you're ever likely to come across.
As you're only going for four days I'd keep it very, very simple, one pot meals are good but allow extra time in the oven. Salads are also good, as is pasta with a jar of sauce maybe with garlic bread, anything which requires the minimum of actual cooking.
Perhaps work out in advance what the four of you actually like and make a menu plan for the four days, including one takeaway.