Must take (apart from the obvious things like passports, tickets):
Blu-tack to hold the plugs on the wall
Cable-ties to lock the cases when returning
Fishermans scales to check the weight of the cases
Travel size shower gel and shampoo - that way you can freshen up when you first get there before going out to buy full size
2 big jars of coffee - can't find a decent cup of coffee and we love coffee!
2 small soft pillows - stolen from a hotel in the UK ages ago and only used when we go on holiday
Very comfortable footwear (Crocs every time)
Camera
Bum/body bag for money etc
Bags for laundry
Sense of humour
Big smile
And the essentials:
Hair straighteners
Make up
High heels