Onion - plus carrot, white cabbage, salt, pepper, raisins and peanuts with yoghurt and mayo to bind. Best made the night before so the peanuts have a chance to lose a bit of their crunch. Just need a baked potato and a barbecue now, but unfortunately it's a bit cold for getting out in the garden.
If you like onions, then add them, otherwise just use cabbage, carrot and mayo ! I often add some shredded apple as well as a red onion, white cabbage, grated carrot and home made or store bought mayonnaise. Mind, I had a cheese baguette with red onion coleslaw recently where the chef had added cream to the coleslaw and it tasted horrible - really nasty and bitter ...why ? no idea !