Not forgetting Warning Triangle, fluorescent waistcoats for each member in the vehicle, headlight deflectors and I believe spare lamps.
Take plenty of gas to last the journey and a very long power lead if you stop at campsites, aires etc
A sense of humour is great, getting lost can mean that you see areas that otherwise you'd have missed.
A satnav can mean that when the unexpected detours occur the sense of humour does not evaporate when you can't find a camp site!
Enjoy yourselves!