We did Haven 2 years ago, me and BF plus 4 boys ageing from 2 to 6. What were thinking? 
I took a laptop so 2 youngest could watch 1 DVD, 2 oldest could watch another.
We took lots of wine.
Took their scooters.
Take 2 sets of swimmers and towels so you can use the swimming pool complex more than once without having to do any washing.
It will be Halloween, so we took games to play (a bucket plus apples to do dunking, extra loo roll to play dressing up as mummies, face paints etc). Take halloween dress up outfits too, as the parks often do a fancy dress event.
Take extra loo roll anyway.
Take a bath mat, a drying up cloth or two, a cloth for the sink, a hand towel for the bathroom
Bake a fruit cake and a banana bread for snacks
We also took pens, colouring books etc
Have fun. We go to Butlins each October half term now, and packing has stayed essentially as above!