OWNER PULLED INTO REST STOP GOT OUT TO GO THE RESTROOM WHILE WIFE GOT THEIR 14 MONTH OLD AND 4 YEAR OLD OUT AND PUT THEM IN THE PASSENGER FRONT SEAT TO FEED THEM AT THIS TIME THE FONT PASSENGER DOOR WAS OPEN WITH THE UNDER DASH COURTESY LIGHT ILLUMINATED FOR ABOUT 10 TO 15 MINS APPROXIMATELY AS WHICH TIME THE DOOR WAS SHUT AND THE CAR PULLED CLOSER TO THE REST STOP AND THE OWNER GOT OUT AND HAD A SNACK LEAVING THE VEHICLE FOR APPROXIMATELY 30 MINS WHEN HE RETURNED AND OPENED THE DRIVER DOOR HE SAW SMOKE IN THE INTERIOR COMING FROM THE PASSENGER SIDE FLOOR BOARD AREA. HE OPENED THE PASSENGER SIDE DOOR AND OBSERVED A PILLOW AND A WOMENS PURSE LOCATED IN THE FLOOR BOARD WITH THE PILLOW SMOKING AND FALLING APART. HE PULLED THE FLOOR MAT OUT ON THE GROUND WITH THE PILLOW AND PURSE ON IT AT WHICH TIME THE PILLOW BURST INTO FLAMES. AFTER REMOVAL OF THE PILLOW WHICH WAS THE SOURCE OF THE SMOKE FIRE DAMAGE AND MELTING WAS NOTED TO THE AREA OF THE UNDER DASH COURTESY LIGHT ON THE PASSENGERS SIDE OF THE VEHICLE.