If you are looking to be in like the autosalon... then do whatever makes a splash....
BUT
If you a looking for a show and shine comp, then other than an extremely clean car (make sure you clean under rubber seals, under floormats, in all exposed areas, under numberplate, in gaps etc) but a first aid kit, a reflective triange, jack, spare tyre, and owners manual were all things i was told about by judges. They look highly on safety and responsibility as well as the overall car.
Good Luck
Mr Sniper911