It would need a really overzealous customs officer to take exception to the small amounts of food for personal consumption in the caravan fridge. Besides, the contents of the fridge will never come into contact with anything or anyone other than the occupants of the vehicle itself, so where is the danger?
In over 60 years of crossing the Channel, including 35 years of towing the caravan, I‘ve never been asked about the contents of the fridge or food within the car, neither on the French side nor upon entering the UK, even during genuine emergencies such as the bird flu or during the BSE outbreak.